Glass box is replaced with 'brick pyramid', while Tate director admits credit crunch could delay completion beyond 2012

Tate Modern has unveiled a subtantially-redesigned upgrade of its 拢215m Herzog & de Meuron extension.

But Tate director Sir Nicholas Serota admitted that due to the slowdown in the financial markets, the extension may end up being completed up to two years after the original opening date of 2012.

As revealed by 好色先生TV in April, the original 鈥渟tacked glass box鈥 has been scrapped in favour of a 鈥渂rick pyramid鈥 which the Tate says is more flexible than the previous design. The scheme will have to be resubmitted for planning.

Serota said of the designs: 鈥淚 don鈥檛 have any problem changing my mind when I see something more mature鈥 it is a more mature response to the brief than the original building.鈥

Jacques Herzog, the scheme鈥檚 architect, said of the decision to use brick: 鈥淚t鈥檚 a cool material. It鈥檚 not used much any more by anybody. We鈥檙e happy about the change in material, and we really think we can use it in a new way.鈥

The extension will also now renovate gigantic oil tanks beneath the former power station as art and performance spaces similar to the museum鈥檚 turbine hall.

As a result the extension will add an additional 21,500m2 to Tate Modern鈥檚 existing 35,000m2 and allow up to 7 million visitors a year to enjoy its galleries.

Construction of the scheme, by construction manager Mace, is expected to begin in June 2009, but Serota admitted that it could be 2014 before the scheme is completed if the building is affected by the credit crunch.

He said: 鈥淭his is the most challenging time to get money, but we are talking to individuals who have the ability and the will to help.鈥

Serota said that the museum has already raised about one-third of the funds to build the 拢215m extension.