Architecture: Why the nuns don't dare leave the house: The owners of Holmwood want to move, says Jonathan Glancey. But they are at the centre of a conservation battle over their suburban Glasgow villa

The Sisters of Our Lady of the Missions are keen to leave Holmwood, their Glasgow home for the past 34 years. They would have left by now if a suitable buyer had appeared on the scene, but Holmwood is the finest and most important house designed by Alexander 'Greek' Thomson, a brilliant, if unjustly obscure, Greek Revival architect, and they have decided to stay until its future is settled and in the right hands.

They do not like having to cope with the vandals and arsonists who have prowled the grounds and outbuildings since they closed the school in the grounds in June; but they know that once they abandon the house itself it will become a rallying point for vandals and thieves.

Now the nuns have found themselves at the centre of a fierce conservation battle. In 1990 a local developer, the Carvill Group, acquired an option to purchase the whole site, and it wants to fill the landscaped grounds with blocks of flats. Only if it wins planning permission for these will it hand over the money that will allow the nuns to move.

But, even while the council deliberates, conservationists have been lobbying the National Trust for Scotland in the hope that it will buy this important Victorian house for the nation, restore it to its Neo-Grecian splendour, open it to the public and put paid to the development proposals. Both the council and the trust are about to make their respective decisions. The nuns will hopefully be able to move either way, although they would like Holmwood's future to be in the hands of the conservation angels.

What Glaswegians and everyone else needs to see is just how important Holmwood (1857-58) is in the history of 19th-century architecture. It is not a large country house although it is the largest house that Thomson designed; it is more a grand suburban villa. Like later suburban houses, its plan is asymmetrical and its roofline low. Based partly on the Neo-Grecian villas of Schinkel and anticipating the 'prairie' houses of the great American architect Frank Lloyd Wright by at least 40 years (these were characterised by their open-plan interiors, low elevations and lack of pseudo-historic detail), Holmwood was an unusual design in an age that balanced chaste Classical symmetry with spikey Gothic Revival fantasy.

The house was probably designed as a wedding present for the son and daughter-in-law of James Couper who owned the Millholm paper mill. Couper allowed his architect a free hand in the design and decoration of this generous present, so much so that Thomson was responsible for every last detail.

Today, although Thomson's decoration at Holmwood is hidden, it is not lost, while just one architectural feature - a chimneypiece - has been removed. The house has been swaddled in swirling wall-to-wall carpets by the sisters. Strip away the Sixties ceiling lamps, the plastic-covered furniture and the coal-effect electric fire and you will see the original panelling and plasterwork and the fine Grecian details on windows, ceilings and fireplaces. The interior of Holmwood is almost as Thomson left it 135 years ago.

Without the intervention of the Alexander Greek Thomson Society (founded in 1991, it has a membership of 400), the developer might have received planning permission by now, built the blocks of flats, obscured Holmwood and allowed the Sisters of Our Lady of the Missions to move out in peace.

The society was set up to promote interest in Thomson (1817-75), who had been all but forgotten while the younger Charles Rennie Mackintosh (1868-1928) - Glasgow's greatest architect - had been restored to fame in the Seventies. Thomson is best known (when he is known) for the highly inventive Neo-Classical churches, terraces and commercial buildings that he designed in central Glasgow, most of which are in a distressing state of faded grandeur. Many architectural historians now rank him, along with the famous Prussian architect, Karl Friedrich Schinkel, as the finest of the 19th- century Neo-Classicists inspired by ancient Greece.

Glasgow has a notorious tradition of ignoring its best architects. Only since the Charles Rennie Mackintosh Society was founded in 1973 has Mackintosh become famous outside specialist circles and his buildings spared destruction. It is now almost impossible to find a news-stand in Glasgow that does not sell postcards featuring Mackintosh buildings or a tourist brochure of the city that does not sing the praises of his Willow Tea Rooms and the Glasgow School of Art.

'Greek' Thomson could be an equal draw, but not perhaps until a major exhibition of his work is held in Glasgow in 1996. By then, unless protective action is taken in the next few weeks, Holmwood could be all but ruined.

The Carvill Group's original plan was to redevelop the grounds with 60 new flats, which would have involved the demolition of the stable block - an integral part of Thomson's design for Holmwood - and the virtual destruction of the carefully landscaped setting. There were no specific plans for the house itself.

The fledgling Alexander Thomson Society went into action and, after discussions with every interested body - the Carvill Group, the National Trust for Scotland, Historic Scotland, Glasgow District Council, Strathclyde Regional Council and the Glasgow Development Agency - reached a compromise. A more modest development of flats was proposed which would leave the house and the best views of it intact. Yet conservationists agree that this solution would still ruin Thomson's composition and spoil, too, the possibility of Holmwood becoming a successful tourist attraction like Mackintosh's unspoilt Hill House in Helensburgh on the outskirts of the city.

So what is likely to happen? The National Trust for Scotland is keen to buy the house, but the purchase price will remain unknown until Glasgow District Council decides whether or not to grant planning permission for Carvill's development within the grounds. The developers might then pull out.

The National Heritage Memorial Fund has said that it is willing to help buy and restore the house (because the nuns have looked after Holmwood well, the cost of restoration is estimated at a relatively paltry pounds 300,000), but only if there is a guarantee that the grounds will not be developed.

The National Trust for Scotland says that it will make its final decision whether or not to fight for Holmwood at the beginning of next month. But what everyone concerned is waiting for is for Glasgow District Council to decide for or against the Carvill Group's planning submission.

Whether the developer pulls out or not, no one wants the house to be left empty. This is not simply because the house is likely to be vandalised, but because, as Gavin Stamp, founder of the Alexander Thomson Society, says, 'in Glasgow, old buildings often demonstrate a curious tendency to 'go on fire' '.

Everything hangs in the balance, which is exactly the situation that allows great architecture to slip through the net and into oblivion. Glasgow has seen so much of such loss through indifference and procrastination that it is a wonder any of the work of Mackintosh and Thomson survives.

Holmwood is too good to be spoilt. The council should find against the development proposals, the National Trust for Scotland should buy the house and with the help of the National Heritage Memorial Fund restore it and open it to the public. If and when that happens, Glasgow will be astonished by the number of visitors who will make the journey from across Europe and the United States to see one of the most significant 19th-century houses: the finest suburban villa of all. If Glasgow allows Holmwood to be spoilt or vandalised in any way, it will regret its indifference before the decade is out.

(Photographs omitted)