I am sure the word biodiversity will sound odd to those children, and I can't help thinking that we really have made life awfully difficult for ourselves with terms like 'sustainability', 'biodiversity' and 'Local Agenda 21'. They don't exactly provide many clues to the uninitiated about their meaning!

Secretary of State, distinguished guests, ladies and gentlemen, I couldn't be more delighted that there is to be an international seminar on biodiversity taking place tomorrow in London, and that this is attracting so much interest. I think I am delighted to have been asked to speak here tonight - though time alone will tell whether the Secretary of State remains pleased to have asked me! If he doesn't, it will be because I have interpreted a little too literally the tradition that after-dinner speeches can be both frank and free-ranging...

For this particular audience, I hope we can take it as read that the Earth Summit in Rio was a most significant moment in history, that Agenda 21 and the Biodiversity Convention were major steps forward, and that the UK Government's response has been admirable. I think we could also agree that the idea of European Nature Conservation Year, with its theme of 'look to the future, look after nature', has a part to play in raising public awareness - and in this context I am delighted to announce that there is to be a biodiversity competition for children.

I am sure the word biodiversity will sound odd to those children, and I can't help thinking that we really have made life awfully difficult for ourselves with terms like 'sustainability', 'biodiversity' and 'Local Agenda 21'. They don't exactly provide many clues to the uninitiated about their meaning! Indeed I am told that some people thought biodiversity was a new sort of washing ingredient! Now I remember the Secretary of State telling a group of people that sustainability was rather like an elephant. Putting aside images of a large grey beast rampaging through Whitehall, crushing non-green Ministers and officials underfoot, he went on to explain that both were difficult to describe, but you would know one when you saw one!

Even that test doesn't apply to biodiversity, but without it I wonder what sort of material and spiritual state we would be in? The interplay of a whole kaleidoscope of species provides our life support system, our food, our medicines and a large part of the beauty that inspires most of us. The problem is that almost all of the actions of our society affect the biodiversity that sustains us. Urbanisation turns green land into concrete; transport systems bisect the countryside, bringing noise and disturbance where once there was tranquility (and let's not forget that any kind of tranquility will be at an immense premium in years to come). Pollution directly reduces the capacity of habitats to support life; modern agriculture has transformed most of our countryside, and the discharge of greenhouse gases leads to global warming and a shift of tolerance zones. Somehow all these points need to be got across, so I couldn't be more pleased that the report of the Biodiversity Steering Group is to be published tomorrow. I hope it will add greatly to public understanding of the central importance of these issues.

Having had a preview of the contents, I do congratulate John Plowman and his group on a thoroughly positive, readable and balanced report. I know it can't have been easy to get everyone to agree this far, and there is at least one interesting omission in the list of Departments taking part. I understand that they wouldn't even have needed to get on their bicycles to attend the meetings...

This, of course, typifies the problems that governments have in dealing with the environment as a cross-sectoral issue. And having met more than a few Environment Ministers in my time, I can tell you that the problem is the same all over the world. The relevant plans are written, or at least led, by Environment Departments, yet any measure of success will be heavily dependent on what happens - or doesn't happen - in Departments of Agriculture, Forestry and Transport - not to mention Treasuries!

Integrating environmental requirements with such potentially conflicting functions is difficult enough at the best of times, but becomes impossible when environmental issues are seen as inconvenient obstacles to be by-passed (if I dare use that word!) with as little disruption as possible to normal service. I have often wondered whether a (relatively!) tame environmental expert working in each department might not make a difference, but for some strange reason it has never been a popular suggestion...! Why not, as a result of this report, have a biodiversity adviser in each department?

Having got that off my chest, I want to commend the report for its scope, its attention to detail and its rational approach. It seems to me entirely admirable that we now have clear objectives and targets for conservation in this country. Without the clarity and focus that targets bring, and without full backing for their delivery, it is hard to see how the disastrous loss of species and habitats from our countryside can be stemmed. I am sure I will not be the only person watching intently to see how the Secretary of State responds, and indeed how much success he can achieve in arguing the case with his Cabinet colleagues...

Now, I don't know about you, ladies and gentlemen, but I do not want to be accused by my grandchildren (if I live long enough to see them!) of sitting idly by and doing nothing while the biodiversity that my generation inherited was being destroyed by short-term short-sightedness and crass insensitivity. History is full of such cases, so let's break the mould. It will be the last chance we've got...

We now have both the science and the Action Plans, and all the research tells us that really large numbers of people do notice and care about such diverse things as the virtual disappearance of the corncrake, a shortage of skylarks and being unable to remember when they last saw a wild orchid.

They might not recognise the term 'biodiversity', but they mind about the loss of ordinary countryside features - through sprayed verges, drained watermeadows, felled copses or farming monocultures - and they know that all these things mean less of the birds, plants and insects that help to make this country special. Raising public awareness, as the report says, will be crucial to success. I am not advocating a revolution, but if the whole community of gardeners, ramblers, birdwatchers, anglers, naturalists and so many more were to make their views known, the results might be impressive.

In this context, I find myself, once again, wanting to pay tribute to the voluntary conservation and landscape protection societies, both here in the UK and more widely. They have provided much of the drive on this issue, which is exactly what Agenda 21 demands, and I hope their members will be suitably heartened by their achievements. The Royal Society for the Protection of Birds' report on the strikingly sharp decline of farmland birds in Wales is a perfect example of the sort of detailed, professional and pervasive study which our NGOs do so well.

Equally, I admire the willingness of the Department of the Environment to work in partnership with the NGOs. I only wish such genuine commitment to Government working together with the voluntary and private sectors, in the national interest, could be found throughout our society. Many people here tonight will know that this partnership approach - and willingness to listen - has been a strong feature of Derek Osborn's time at the Department, and I only hope it will survive the transition to his new and splendid responsibilities as Chairman of the Council of the European Environment Agency, and elsewhere.

Partnership helps a great deal in identifying problems and achieving solutions, but the causes of loss of biodiversity can often be traced to public policies, and economic ones in particular. The best (by which I mean worst!) example is undoubtedly the Common Agricultural Policy. Within the European Union the public pay around £30 billion a year for production methods which have little or no respect for wildlife or landscape.

Not surprisingly, the Ministry of Agriculture's CAP Review Group has concluded that radical reform of the CAP is needed. Their report notes that agricultural policy should recognise its impact on the environment, including wildlife habitats and species diversity, by setting clear objectives for environmental conservation and management, and giving these much higher priority. And I would add that this need not mean economic difficulties for the farming community. There is plenty of evidence that farmers welcome practical schemes that provide incentives to modify their practices in the right direction, rather than merely setting land aside.

I find this encouraging, but great damage has already been done. To give just a couple of examples, in the last 25 years the annual numbers of skylarks have reduced by one and a half million, and song thrushes by a million. Roughly similar numbers remain, but what will be left in another 25 years time of these species which we take to epitomise farmland?

Of course there are excellent schemes which help some particularly special parts of the countryside, but I am not alone in believing that we urgently need new measures that will tackle the continuing deterioration of the countryside as a whole, and indeed this point comes through strongly from the recent Rural White Paper. What is sustainable about modern farming practices which do not support widespread populations of skylark, song thrush, lapwing or grey partridge - and the plants and insects that support them?

I don't believe you need a degree in Ecology to recognise that the rich biodiversity of the British countryside has evolved over many hundreds of years. It has been shaped and maintained by traditional farming practices which have respected the capacity of the land and natural cycles, but are now being superseded at an alarming rate, almost everywhere, by farming on an industrial scale. Like so many 'modernist systems', this approach relies on constant innovation and frenetic competition. And it is certainly not going to do anything for the wildlife which evolved in a gentler and more sustainable era. But I don't suppose there is much hope of anyone being encouraged to stand up and teach that in our agricultural colleges?

The 1992 CAP reforms appear to have made only a slight improvement to farming's environmental impacts. The establishment of the agri-environment package was a significant step forward, in principle, but the overwhelming emphasis on production still works in the opposite direction.

The next source of pressure, and opportunity for reform, will be the eastward expansion of the European Union. The choice we face from a biodiversity standpoint is simple. Can we seize the opportunity to redefine the CAP radically, giving it new and clearer environmental objectives and systems of operation? Or do we simply, unthinkingly, extend the CAP as it stands, allowing the damage to our own wildlife to continue, while subjecting some of the most environmentally-sensitive and rich countryside in central and Eastern Europe to the same mistakes?

Farming is, of course, the major land use over much of the Earth's surface and, without careful planning, will always tend to reduce biodiversity. This is nothing new, or even particularly alarming. What is alarming is the rate of change and the degree of agricultural specialisation. During this century some 75 per cent of the genetic diversity of agricultural crops has been lost. Only about 150 plant species are now cultivated for food on any significant scale, and just three of those supply almost 60 per cent of the calories derived from plants. In India more than 30,000 rice varieties were once grown. Now just ten cover 75 per cent of the whole rice area. In the Netherlands a single potato variety covers 80 per cent of the potato fields, and in France 71 per cent of apple production consists of one variety - Golden Delicious.

It is only comparatively recently that fields consisting of a single species or variety have become common, usually as a result of incentives based on cheap and readily-available inputs. And the pressure to adopt high-input, high output solutions to food shortages remains remorseless with, not surprisingly, strong encouragement from the agro-chemical companies who stand to gain most. A vast body of research underpins this approach, culminating recently in a book entitled (and I am not joking) 'Saving the planet with pesticides and plastic'.

Yet it is possible to obtain substantial increases in yields through sustainable technologies and practices, which just happen to enhance rather than erode local biodiversity. The only thing that has to be spread and applied more intensively is knowledge. In Honduras and Guatemala, for example, farmers using green manures have tripled their food yields. Equally importantly, they have diversified their farms - many now grow 25 different crops where ten years ago they grew only maize.

In countries as diverse as Indonesia, Bangladesh, Kenya and Brazil, several tens of thousands of farmers have in the past three or four years adopted more sustainable approaches to agriculture. All have substantially improved their food security, without resorting to large amounts of agro-chemicals, and I am happy to say that some of the best examples result from the efforts of our own Overseas Development Administration and the NGOs with whom they work so well.

One of the great advantages of such systems is that they permit the survival of wild resources of immense value. We need to recognise that the inbuilt resilience of nature - which enables it to adapt to pressures such as pollution or climate change - depends in part on the availability of a wide diversity of genes and species, so that as some are run out of the race others can take over. But the supply is finite. We can destroy in seconds what has taken tens of millions of years to evolve.

Crop breeders continually need to go back to the wild species to find new characteristics that will make the strains we cultivate more robust, or better in other ways. A 'useless' wild wheat from Turkey recently conferred disease resistance on cultivated strains worth $50 million a year in the USA alone. Drugs from plants trade at around $43 billion a year, and there are more to be found out there.

There are, of course, plenty of people (not all employed or supported by the agro-chemical industry) who see genetic engineering as the most promising way forward for agriculture. And it is certainly one way of maximising the use of our total genetic resources.

But am I really alone in feeling profoundly apprehensive about many of the early signals from this brave new world, and the confidence - bordering on arrogance - with which it is promoted? When I read that most of the genetically engineered species released so far in the USA have been billed as 'new crops for old herbicides', having been developed by the major agro-chemical companies seeking farmer-loyalty to their own particular weed-control chemicals, my heart sinks at the prospect.

And how much biodiversity would the scientists here tonight expect to discover in a field of genetically-engineered sugar beet, after the regular applications of the 'Roundup' to which it alone is resistant? And if these applications of genetic engineering are not enough to send a cold chill down the spine, then I suggest that you take a look at the situation in China, where such releases are already routine, with minimal controls on a vast scale.

I am not, for a moment, decrying all uses of such technologies, nor do I believe that the controls which exist in this country are anything other than adequate to the perceived risks. But as a strong supporter of the precautionary principle, I think it is timely to recall the almost entirely damaging effects of introductions of alien species to new environments.

It is too late to ask those responsible whether they really thought it was a good idea to introduce the rabbit and the cane toad to Australia, or the grey squirrel to this country. And botanists would add, the introduction of the goat almost anywhere! But I am quite sure that whoever permitted the introduction of non-native species of crayfish to this country thought they were doing the right thing - helping farm diversification, boosting rural employment, reducing imports - the case must have been unassailable in bureaucratic terms.

Yet those species have brought with them disease and competition such that our native white-clawed crayfish now finds itself on the list of threatened species, and the introduced varieties are dining happily on the eggs of Scottish salmon - with vastly greater potential impacts on rural employment and the other problems they were imported to help solve.

When I read that pollen from genetically engineered oilseed rape travels much further than had been predicted from early experiments on small plots, and that the scale of pollen release in a commercial situation had been 'grossly under-estimated', I can't help thinking back to those crayfish. I don't suppose anyone thought they would travel very far either... Is it fair to ask whether anyone has given any real thought to what to do if (and I know it is only an 'if') herbicide-resistant crop plants spread to become weeds in fields of other crops? Won't the inevitable answer be new and stronger herbicides, leading to further reductions in biodiversity?

Ladies and gentlemen, I do think we sometimes need to remind ourselves that our own species has become immeasurably more powerful than any that has ever existed on Earth. We have transformed the face of the land and spread our pollution far and wide, but surely we have, somehow, to find the space and maintain the conditions in which a wide variety of other species can flourish and evolve?

I happen to believe that technology should be the servant of mankind and not the master. But this is rapidly becoming a minority view in a society where any new technological ability is rapidly put into practice, with only the most cursory glance at the wisdom and ethics of doing so. The idea of restraint is decidedly old-fashioned, and the role of God in the wider scheme of things is rapidly being usurped by the worship of technology. Yet can we really go on behaving in such a cavalier way and still call ourselves civilised and responsible human beings?

I believe that in the face of such threats it is more important than ever for mankind to accept responsibility for the stewardship of the natural world. Some people will see this as a religious duty, since all living things are the works of God; others will see it as a simple human duty of care towards the Earth and the living richness that sustains us, and a further group will take the view that we and our descendants will be immeasurably the poorer if we destroy the wonders of nature to satisfy our short-term needs. But the conclusion reached is the same in each case.

If we set ourselves to achieve a truly sustainable process of development and a sustainable style of living, one of the most important indicators of our success will be how well we safeguard the living diversity of the Earth, on this and other continents. Biodiversity is a key test of sustainability.

In addressing this task we have some important strengths in this country, including a long tradition of nature conservation; active, articulate and effective NGOs; particularly strong and well-connected scientific institutions (including the Natural History Museum and the Royal Botanic Gardens of Kew and Edinburgh), and a range of international links, especially within the Commonwealth.

Those strengths equip us well to work in partnership with the developing world, so that those countries can sustain and benefit from their own biological resources. And those partnerships should not be without economic value to both partners, given the value that we now recognise in those biological resources.

But, above all, I hope we can increasingly come to recognise that Nature is not just something to be used, or traded, but is an essential part of the same web of life as ourselves - part of our wider being. In safeguarding biological diversity, however we define it, we safeguard ourselves, in a practical, spiritual, aesthetic and ethical sense.

So - I wish you all a most productive conference tomorrow, and will greatly look forward to hearing the results.