Bath could be stripped of its status as a World Heritage site if a massive new development of tower blocks, homes and offices goes ahead.

Developers want to build on an 87-acre site near the city centre. The £1 billion project would be the largest development in any World Heritage Site.

Bath was granted its status by Unesco in 1987 because of its spectacular and still largely intact Georgian architecture. The Bath Western Riverside Project, on the site of a former gasworks, would significantly alter the skyline of the city.

The developer, Crest Nicholson, won planning permission from Bath council by just one vote in January and the plans are awaiting approval from Ruth Kelly, the Secretary of State for Communities and Local Government. Conservation groups have objected to the development, claiming that its style is out of keeping with the rest of the city. The International Council on Monuments and Sites monitors the 830 World Heritage Sites on behalf of Unesco. Its secretary in Britain, Susan Denyer, said that the development would break guidelines that are designed to preserve the character of the city.

She said: “We are extremely concerned about the impact the Bath Western Riverside site could have on the outstanding universal value of the city and raised objections.

“It would impact adversely on the rather wonderful skyline of Bath and the beautiful valley that surrounds it. So large a project on such an important site should be developed in an exemplary way, where we can be proud of what has been achieved. If completed we would have to pass on our serious concerns to the World Heritage Committee. If it is felt that the outstanding universal value of the city has been lost, then it could lose its status.”

The Western Riverside is one of several major regeneration projects in progress or being planned in Bath that have alarmed conservationists.

Local residents have fought to save Churchill House, a Neo-Classical landmark earmarked for demolition to make way for a new bus station. Campaigners claim that the ultra-modern glass and metal structure scheduled to replace it resembles a tin of baked beans.

James Dyson, the vacuum cleaner entrepreneur, has plans for a £25 million design school at South Quay, near the city centre. The city is also waiting to see whether the council will allow Bath Rugby Club to spend £16 million expanding its city-centre stadium.

The last World Heritage Committee review of Bath, in 2006, said: “Georgian Bath is important, not for events of momentous importance, but as a setting for social history. The residents and visitors to this national health resort form a roll call of the aristocracy, the gentry and their attendants on the one hand and of the artists, authors and dramatists they patronised on the other.”

A spokesman for the Department for Culture, Media and Sport said that a city should adapt to suit its inhabitants’ changing needs. “Stringent local planning guidelines are in place to protect the many listed properties in the town. As for its World Heritage Status, that is a matter that Unesco oversees,” he added.

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