The building is a London landmark

A celebrity party on 15 April will herald the launch of the Saatchi Gallery, at the County Hall, before it opens to the public two days later.

Set between the sites of the two Tate galleries, Tate Modern and Tate Britain, the South Bank venue will house some of the world's most important contemporary works of art.

The gallery will open with a retrospective of works by Damien Hirst. Exhibitions from Tracey Emin, Sarah Lucas and Jenny Saville will follow.

County Hall was home to the capital's local government until 1986 when the Greater London Council was abolished.

'Extraordinary rooms'

It was designed by Ralph Knott and completed in stages between 1922 and 1933.

The building is now also home to enterprises including the London Aquarium, a Salvador Dali exhibition, two hotels and several restaurants, and has been joined by the adjacent London Eye ferris wheel.

Mr Saatchi, who made his fortune in advertising, said last year: "The extraordinary rooms in County Hall will make an interesting setting for works like Hirst's shark and Emin's bed.

"I don't want the artists I believe in having to wait until they are pensioners before the public has a chance to see their works in large scale shows."

The Saatchi gallery will be just a short walk upriver from Tate Modern, which has been credited with helping bring new investment to the south bank of the Thames.

Like the Tate, the Saatchi gallery will open late two nights each week.

The new gallery has been seen by some as a direct challenge to the Tate, but executives there say they will welcome a new museum on the South Bank.