Designs for a controversial extension to Tate Modern have been given the go-ahead.

The plan, by architects Herzog & de Meuron, was unanimously passed by Southwark councillors overnight.

Tate director Sir Nicholas Serota said: "We are delighted...this decision would not have been possible without the involvement and support of local residents, which has been crucial to the development of the design. We look forward to bringing to Southwark a landmark building for the 21st century."

The £215million proposal takes the form of a collection of glass boxes stacked in a pyramid and would stand 250 feet tall.

It would increase gallery space by 60 per cent, which directors say is urgently needed. It had more than five million visitors in the past 12 months, almost three times the expected level.

A gallery spokeswoman said: "A spectacular new building will be created on the south side of the existing gallery to provide more space for modern and contemporary art."

But the plan has been criticised for its impact on one of London's landmark sites. The Twentieth Century Society described the design as "hotchpotch" and architectural historian Gavin Stamp said it would be a "gratuitous disfigurement" to the original building.