The tower will be 200 feet higher than Canary Wharf

The proposed tower, which has been designed by architect Renzo Piano, will appear as a slender spire of glass with steeply sloping faces made of large shards of "extra white glass".

This combination will make the tower seem partly to disappear into the sky and it is likely to change its character and appearance with seasonal variations of light and weather.

There will be three public viewing areas in the tower, including the top three floors.

A large, canopied, public space at the bottom of the tower will also be created under the scheme which will be on the current Southwark Towers site.

Southwark Council said it was likely the tower, which will be 200 feet (61 metres) higher than the UK's current tallest building, Canary Wharf tower, would become a symbol of London.

It has received the backing of the Greater London Authority which has drawn up policy on skyscrapers in London.

It would become a picture postcard image representing London

Commission for Architecture

Commenting on the proposal, Mr Livingstone's office said it would "deliver architecture of world-class quality, which will positively contribute to London's world city image and the London skyline."

It did not believe that St Paul's Cathedral or other nearby heritage sites would be damaged by the skyscraper plan.

The Commission for Architecture and the Built Environment (Cabe), the government design watchdog, has also praised the proposal.

Cabe said the building "would inevitably assume iconic status.

"It would be visible from near and afar, from many different places, dominating many views.

"It would become a picture-postcard image representing London."

However, English Heritage, said the Tower of London World Heritage site would be compromised by the skyscraper which would be visible from inside the fortress.

The tower is being built in the City of London

It said views of St Paul's Cathedral from north London would be dominated by the skyscraper and Tower Bridge and other nearby historic buildings would be dominated by the tall building.

The man behind the ambitious scheme says the building is needed to provide office space in the City.

Entrepreneur Irvine Sellar said: "There is a shortage of quality office space, but more than that I think London deserves a global landmark of this sort."

Southwark Council's development control committee gave approval for the skyscraper at a meeting on Monday, with conditions.

Although the government has the right to call the application in for greater scrutiny, a spokeswoman for the council said it was thought unlikely because of the backing from the mayor of London.