British Museum reveals its £135m extension

Under designs drawn up by Lord Rogers's architecture firm, the museum will build three pavilions on seven levels. This will create 1,100 square metres of gallery space to hold shows such as China's First Emperor and Hadrian's Empire And Conflict.

The plan will be submitted to Camden council within the next two weeks and museum director Neil MacGregor has revealed that two-thirds of the funding has already been found.

At least £22.5million has been pledged by the Department for Culture, Media and Sport while an anonymous donor is believed to have made one of the largest ever private donations to a museum.

Mr MacGregor said he is confident he will raise the remaining £45million. "We're very hopeful that people will want to join in because this is about the protection of the cultural patrimony of the world," he said.

Visitors to the new pavilions will see "ghostly activity" through cast glass walls that will give a mottled, semi-transparent effect.

Graham Stirk, the architect in charge of the project, says that the building "will change its moods" in different light. The plans, the most dramatic since the creation of the Great Court in 2000, and the greatest extension to the museum for almost a century, include conservation workshops, and a lift capable of bringing large trucks loaded with objects into underground storage areas.

It will entail the demolition of two reproduction Georgian houses, built in the Seventies, on Montague Place. Some conservationists have criticised this but English Heritage say the plans are a "first class architectural response" to a "sensitive setting" although there "remain areas of detailed design" they will discuss.

The Commission for Architecture and the Built Environment also supports the scheme. The expansion is designed by Rogers Stirk Harbour and Partners, the practice led by Lord Rogers of Riverside. Lord Rogers made his name with the Pompidou Centre in Paris in the Seventies, and this will be his practice's first completed museum or gallery since then. The museum says it is continuing a tradition of "always working with the greatest architects", which goes back to its original architect Sir Robert Smirke and includes Lord Foster, who designed the Great Court.

The model of the proposed building will go on public display at the British Museum this Friday. It is hoped the project will be completed by 2012.

The scheme will raise again the question of what to do with the famous circular Reading Room at the centre of the museum, which has been underused since the British Library moved to Euston Road.

The Reading Room is currently adapted for temporary exhibitions, but these will be housed in the new building. The British Museum admits it does not know what to do with the room, and is open to suggestions.