It is a former seminary described as one of the most important modern buildings in Europe, but has been left abandoned and vandalised for more than 25 years.

Now, however, the derelict St Peter's Seminary in Cardross, a modernist building which lies as an empty eyesore, could be in line for a major makeover.

A leading commercial developer has made a firm offer to buy and renovate the decaying masterpiece, which was designed by lauded Glasgow architects Isi Metzstein and Andy MacMillan.

Significantly, The Herald understands that the official conservation report commissioned by the Catholic Church for the site stresses the architectural and cultural importance of the building and says it should be more than just "mothballed" as an inconvenient ruin.

The seminary, which closed in 1980, is A-listed and earlier this year was included on the 100 most endangered sites by the World Monument Fund, while Historic Scotland have said it is "one of Scotland's most important twentieth-century historic buildings".

The Church, which still owns the building and site, has lodged plans with Argyll and Bute Council to make the ruin safe, but not for re-use, and build 29 houses on adjacent land.

However, the conservation report is believed to recommend that the building is restored and put to a use. The report, by conservation specialist Avanti Architects, was commissioned in January by the Archdiocese of Glasgow, working with Argyll and Bute Council and Historic Scotland.

Yesterday Mr Metzstein and Mr MacMillan, now both 79, speaking at the launch of a major retrospective of their work for the Gillespie, Kidd and Coia firm at the Lighthouse in Glasgow, said they were less than enthusiastic about the seminary being turned into a hotel - but hoped it could be used again in the future.

Urban Splash, a leading urban developer in Manchester, has made a bid to buy the building from the Archdiocese of Glasgow - which won the Royal Institute of British Architects' Gold Medal - to convert it into a hotel.

A spokesman for the Catholic Church said, however, that no decision on its future could be made until the publication of the conservation report.

The report is due to be published early next month, but one source who has read it said last night: "The report concludes it is a highly significant building and it needs care and attention. That will call into question the current planning application.

"It says the answer is not to mothball' the building. It needs proper thought to its future and a mix of private and public funding to secure its future. It is encouraging for those who wish to see the building put to future use."

Mr Metzstein said he was unsure that the building could be a functional hotel.

"Personally, I think the rooms are too small, and of course there are no en-suite bathrooms," he said, half jokingly.

"My ideal would be to go back 20 years and have it used again as a seminary, but that is not going to happen. But nor do I want it all pulled down and its concrete used to pave motorways.

"I would like it being made into a music centre for young musicians, who could live there in residence and have concerts: but they would have to tolerate less than comfortable conditions."

Mr MacMillan added: "Even in its ruined state it has so much support and admiration. It was designed specifically for a spiritual use: if you fill it full of shops it would take away from that."

The exhibition at the Lighthouse is the first major survey of the two architects' work and focuses on their legacy, including St Brides Church in East Kilbride, the library at Wadham College in Oxford, Robinson College in Cambridge and the series of buildings they designed for the Catholic Church in the 1950s and 1960s.

Nick Barley, director of the Lighthouse, said: "I would just like to see St Peter's Seminary have a future at all. It is one of their greatest designs and right now it is just a ruin.

"However, I do think there is now a belief that the building can be re-used and not just preserved as it is."

The exhibition runs from tomorrow until February 10, 2008.

1966 Seminary opens to first trainee priests 1971 Listed category B by Historic Scotland 1980 Seminary closes, building used as drug rehab centre until 1987.

1992 Listing upgraded to category A 2007 January It becomes the second modernist building in UK on the World Monument Fund's list of 100 most endangered sites. The Catholic Church commissions conservation report by Avanti Architects.

October Hotel plans mooted by Urban Splash. Avanti report, due December, said to advise sensitive restoration.