These inspiring examples show what can be done, and what exciting possibilities there are for many historic buildings.

I recently heard from a leading North Wales estate agent charged with disposing of a historic hospital building. He reported that the only enquiries he had received involved "breaking the site up and selling off the attractive elements". Such asset stripping, he pointed out, would leave most of the hospital's larger buildings unoccupied and decaying. This is a bulletin from the front. It testifies how difficult it is to find a private buyer who can produce a viable and sensitive solution to a historic building of this magnitude. And the story, as I have become acutely aware over the past few years, is repeated again and again across the UK in a desperate catalogue of decay and loss - a loss of heritage but, more importantly, a loss of opportunity.

Changes in the provision of health, defence and education, as well as industrial and social change, have brought a huge mass of important historic buildings onto the market, ranging from redundant military and hospital complexes to imposing mills and warehouses. The private sector is overwhelmed, and regional building preservation trusts are often defeated by the sheer scale of the sites on offer. Finding alternative uses, therefore, poses very real problems for these buildings which stand as monuments to the achievements of previous generations. And while practical solutions evade the owners, the buildings, often well maintained for more than a century or more, stand empty, an invitation to vandals, while restoration and conversion costs increase inexorably, month by month.

Personally I am not prepared to sit back and see this great legacy needlessly squandered, especially as, with a little imagination, many historic buildings can become real assets to their local communities, offering job opportunities and a focus for local regeneration schemes. I have already established initiatives through organisations, such as my Institute of Architecture and Business in the Community, to try to show what might be done. It seems to me, however, that there is scope in this important area for a new initiative.

So a new trust has been set up after a year in which a steering group of regeneration and conservation professionals researched the field. The Phoenix Trust, under my presidency, will act as a larger version of the many successful building preservation trusts, acquiring, repairing and then selling historic buildings to new owners. Unlike the heritage agencies or the national trusts, the trust is not in the business of taking properties into long-term guardianship as show places. Instead it will undertake a form of urban and rural regeneration - transforming buildings into places where people can live, work and enjoy themselves in many different, enterprising ways. It aims to work by practical example, and will not take on properties for which the commercial sector can provide ready and suitable solutions. Our targets are the dozens of major buildings, languishing without prospect of repair or re-use, for which we can make the difference.

The trust expects to have a small number of major projects in hand at any one time - not enough to tackle the whole problem single-handedly, but sufficient to breathe new life into 20 great complexes in as many years. We also hope to inspire others to seek similar sensitive and community-based solutions, and promote the skills associated with historic building renovation and conversion. Sometimes we may be able to achieve the desired results by simply pointing the way, either by preparing plans which encourage others to tackle the job, or by prompting the owners to offer unwanted buildings for sale.

We are immensely fortunate to have as chairman David Taylor, a pioneer in terms of public and private sector involvement in the field of urban regeneration, acclaimed for his work at English Partnerships and now Enterprise plc. Our director is Kit Martin who has a track record second to none in this field.

The trustees will be looking, where appropriate, for lottery and private sector support but, broadly, each project is intended to break even, with costs of repair and adaptation being recovered through sales. Where a building has fallen into a state of near collapse, the proportion of grant aid needed will be higher. Exposure on each project will be limited by tackling one phase at a time, recycling the proceeds from the first sales into the second and third phases where appropriate. The core formula might be termed "enterprise conservation".

Stanley Mills, a spectacular sandstone mill complex on the River Tay north of Perth, is the first project. In desperation, and as a result of serious vandalism, Historic Scotland acquired the site last year, and is repairing the oldest Arkwright-designed mill as a public amenity. It will include a small museum, restaurant and waterside garden. Beside it are two large vacant multi-storey mills. With their broken windows and floors strewn with debris, they look pretty disheartening at first. Yet every window has a glorious view over the river to wooded banks with hardly another building in view. The plan is to convert the mills to residential use, creating houses and flats at a range of prices that will appeal to a local and national market. There is also the possibility of studios and work spaces for those who live in the complex in the much smaller north range, with further workshops and, possibly, a centre for building conservation studies on other parts of the site.

Other potential projects are coming to the trust's attention every day. Regeneration projects suggested (to name but a few) involve a vast domed hospital in the centre of a historic town; a derelict mansion whose surrounding park has already been redeveloped at a cost of many millions of pounds as a major equestrian centre; the historic core of a Napoleonic garrison; a breathtaking, but badly vandalised, hospital group in a vast park set in a dense urban area; decaying military buildings in a prominent dockside complex; and long-disused pithead machine halls whose splendid proportions and design details reflect the dignity accorded by our forbears to industry.

I feel deeply that the craftsmanship, artistry and pride which went into the construction of these places deserves recognition and celebration in an act of millennial renewal. By finding and realising new uses for them, we are building on the achievements of the past, and giving communities all over Britain a chance to use and enjoy assets that would otherwise simply go to waste.

Solutions like these can offer excellent value for money. There is a ready supply of users for buildings converted in the right way, evident in a number of successful projects already completed. The Royal Naval Hospital, Great Yarmouth, is a monumental arcaded Georgian square, and was built to house sailors returning from the Napoleonic wars. It was last used as a psychiatric unit, and there was concern on its closure that this historic complex would be lost amid new housing development. Historic Houses Rescue came forward with a proposal just in time. Some two acres of temporary and prefabricated buildings have now been removed, and all the historic buildings are being restored. There is a range of houses and apartments appealing both to the local and national market, and sustained demand shows how excited people are at the prospect of living in a historic building if they are given the opportunity. There is also a chapel which will remain consecrated, and the building located under the clock tower will be a small museum with an important collection of Nelson memorabilia so that local people and visitors can enjoy the buildings and learn a little more of Yarmouth's story.

Peninsula Barracks, in Winchester, is a magnificent turn-of-the-century complex, laid out around a vast parade ground. It stands on the site of the Norman castle and a larger palace built by Sir Christopher Wren for Charles II which was left as a roofed shell on the king's death and later turned into a barracks. When the Greenjackets moved to new accommodation outside the city, Peninsula Barracks was left empty and decaying. Permission was given to demolish the whole of the Lower Barracks, but SAVE Britain's Heritage, working with local architect, Huw Thomas, drew up a scheme for converting all the buildings for residential use and found a developer to buy the site. The scheme will be complete early next year, with a handsome formal garden replacing the tarmac. The 100 houses and flats have sold well.

Dean Clough Mills, in Halifax, grew from small beginnings to be the town's largest employer. By 1860 it covered 18 acres, and Crossleys employed 5,000 people making carpets. The present buildings contain 1.25 million square feet, much of it in multi-storey blocks. When the mill finally closed in 1983, though listed, it increasingly appeared a lost cause until Sir Ernest Hall came forward with a visionary scheme to create a small business centre, offering start-up space to young people. Within a few years, all the empty spaces in the mill had been filled, and Dean Clough was home to more than 200 small firms with a workforce of more than 1,500. Such was the cachet of the development that major insurance companies moved in, followed by the local VAT man.

These inspiring examples show what can be done, and what exciting possibilities there are for many historic buildings. But time is short; many of the greatest sites are rapidly becoming derelict and vandalised. Others have been demolished already. The approaching millennium, with its twin themes of spiritual and physical renewal, provides a unique opportunity to make the past work for our future.