Tate Modern speeds up plan to build galleries

A grand new vision for Tate Modern, the world's most popular modern art gallery, will see it expand by more than 50 per cent and form the centre of a thriving south London cultural quarter by 2011.

The development has been a long-term aim since the gallery opened five years ago, but will happen earlier than planned because of the need to upgrade an electricity substation, a reminder of the building's origins as a power station.

The construction time needed for the upgrade, required to meet growing electricity demands, will offer the gallery several years to raise the funding, which could be as much as the £135m it cost to create Tate Modern. But Sir Nicholas Serota, the Tate's director, said it would not know the price for certain until plans were presented by Herzog and de Meuron, who devised the original transformation and who have been reappointed for the second phase.

Sir Nicholassaid the Tate had to act because once the power company had built its new plant, it would be a fixture in the southern corner of the gallery for probably the next 50 years. With both residential and commercial developments also transforming the surrounding Bankside area, Tate Modern needed to map out its own requirements or risk losing options.

"We have to bring forward our own thoughts about the way Tate Modern should be completed. If we fail to do so, we will find ourselves constrained by other plans that have already been given planning permission," he said. The aim will be to create a new suite of galleries, including some for video and photography, as well as education facilities and performance spaces for the gallery's growing programme of live events in the southern part of the existing building, which will also get a new entrance. The development will be possible because advances in technology mean less space will be required for the new substation.

Sir Nicholas said the space was needed to show more collections. Many visitors complained when favourite works, such as Cornelia Parker's exploded shed, Cold Dark Matter, were removed to rotate the displays.

The success of the gallery, which has more than four million visitors a year, twice what had been predicted, also put pressure on facilities. It was "unbearably crowded" at weekends, Sir Nicholas said.

He said he expected that far more private money and less Lottery support would be involved than in the original Tate Modern scheme and he hoped both local businesses and international companies would offer support.