Tate Modern has unveiled plans for a tall extension on its south side increasing the modern art gallery's overall size by more than half.
The new glass building, on part of the southwest lawn, will rise above the existing main brick structure and be visible from the City.
The architects are Herzog & de Meuron who converted Bankside Power Station into Tate Modern. The cost of the new building is £165 million at today's prices and the Tate will be seeking both Lottery and private funding. It is estimated that the final bill could be £215 million.
Mayor of London Ken Livingstone immediately announced a £7 million investment from the London Development Agency to help fast -rack the development so that it can be completed by 2012 when SE1's riverside hosts the Olympic Games cultural programme.
The decision by EDF, still operating an electricity substation in the former power station, to move into a smaller area has provided the opportunity for the Tate to bring its long term plans forward.
There will be new performance areas, a 400 seat auditorium, new flexible exhibition space and more room for the pioneering education service. A public roof terrace and a tenth floor restaurant will provide panoramic views both north and south.
The announcement has been welcomed by Southwark Council leader Nick Stanton who, speaking at the press conference, described the Tate as "a bridgehead to economic development" and welcomed the emphasis on community use and space. He also spoke of the opportunity to pull visitors down to the Elephant & Castle.
Tate Director Sir Nicholas Serota confirmed that the Tate's new front door would face south across a piazza looking towards SE1's urban park occupied by at least twenty cultural organisations. Over a thousand new trees will be planted to the south of the building.
Sir Nick agreed that Sumner Street might eventually be closed during at least part of the day and suggested that the new south entrance would open up a north-south pedestrian 'street' through the Turbine Hall for at least twelve hours every day.
The director claimed that the expanded Tate would give Southwark an exhibition programme of international resonance. He said that the Tate had become partners with the community and, having worked with the residential organisations, he believed that there would be a broad level of support for the extension.
The Tate on Bankside has four million more visitors per year than the Guggenheim in Bilbao and twice as many as the Centre Pompidou in Paris and MoMA in New York.
The designs for the new development will be submitted to Southwark Planning in September.