London's Tate Modern art gallery, which has attracted seven million visitors since it opened 18 months ago, has won the first prime minister's award for Better Public Building.

Tony Blair praised the gallery for its part in transforming the London borough of Southwark, saying it had achieved a balance of being "awe-inspiring while still being welcoming and accessible".

The gallery boasts a large Turbine Hall

The award was given by the Commission for Architecture and the Built Environment (CABE), and was chosen by a panel who decided between many buildings commissioned by or on behalf of central or local government.

The Prime Minister's Award is to be made annually to any new building project paid for by the public.

Mr Blair added that the building was "an excellent example of public building at its very best".

The gallery's director, Sir Nicholas Serota, said it was a "marvellous honour" for the architects, consultants and builders who worked on the Tate Modern project.

Louis Bourgeois' 30ft tall spider was displayed in Tate Modern

"We started with the objective of creating a building that would make art accessible to large numbers and encourage new audiences. I think we have achieved this aim," he said.

Tate Modern occupies the refurbished shell of the Bankside Power Station, which was originally designed by Sir Giles Gilbert Scott, the man behind Battersea Power Station, Liverpool's Anglican Cathedral and the old-fashioned red telephone boxes.

It took contractors two years to rip out the power station's boilers and turbines, which fell silent in 1981, less than 20 years after the building was first completed.

Extra floors

Swiss architects Jacques Herzog and Pierre de Meuron, who were chosen to transform the huge brick building, have retained many of its existing features.

Inside the gallery's lobby, the 100ft-high former turbine hall, no attempt has been made to disguise the towering steel columns or industrial brickwork.

The power station's elegant 325ft central chimney also remains, and to either side of this, Herzog and de Meuron have added a glass structure the length of the building.

The addition not only houses two extra gallery floors, but allows for the entry of natural light into the remainder of the building.

Popular

The judges' decision was based on several categories including design, construction, financial management of the project and the relationship it has to its surroundings.

A commission spokesman confirmed that the Tate was recently found to be the most popular art gallery in the world.

"Tate Modern has welcomed more than seven million people through its doors, nearly a quarter of whom said the design of the building was as important a reason for their visit as the art contained inside it," he said.

The award was sponsored by CABE and the Office for Government Commerce.