The Queen told London Assembly members that she hoped City Hall would "provide an exciting forum for Londoners as your debates ebb and flow".

She added: "This new building looks out not just to the City of London but also to the east and south east where so much prosperity and dynamism is found."

The interior brings to mind the Guggenheim Museum

Mr Livingstone said "great premises" had been opened for London's government and, quoting the mayor of ancient Athens, he promised to leave the capital "greater, better and more beautiful".

The mayors of Paris and Berlin and the first deputy mayor of Moscow also attended the opening.

Mr Livingstone will use the occasion to hold a series of meetings with the mayors of these key European cities.

He said: "This is a landmark building. I think it brings home to people there is now a city government again after that long period without one."

The official opening of City Hall will be followed by a carnival parade along the riverside walk.

Technical problems

The �43m building will accommodate 440 staff and members of the assembly.

At its heart is a showpiece debating chamber, above which rises a spiral staircase.

Those keen to view government in action - or simply soak up the city skyline - will be welcome.

As well as 250-seat viewing gallery in the chamber, the top floor of the 45m-high building is an open public space.

City Hall uses a quarter of the energy of a conventional office building, yet some of its hi-tech touches have suffered teething troubles.

Glitches that have had to be remedied include roof vents controlled by weather sensors that stayed open during a storm; glare inside the offices; and high humidity in summer and sudden chills in winter.

Supporters of City Hall say it is one of the most inspired buildings in Europe in years, and a bold statement on transparent government.

Its detractors say that the building has cramped offices, is prone to leaks and is "disappointingly dumpy".