The building, designed by Sir Denys Lasdun, is made up of three theatres. Two, the Olivier and the Lyttleton, are already open with a third, the Cottlesloe, expected to open next year.

Bands, fanfares, an outdoor carnival and fireworks greeted the large crowds who turned out despite the pouring rain.

Funding problems

In 1951 the Queen laid a foundation stone at the site next to the Festival Hall. Official building work did not start until 1969 following a series of funding problems.

The theatre complex was expected to open in 1973 but was delayed due to construction problems.

Before unveiling a commemorative plaque the Queen said: "It stands as a tribute to all those who dreamt of it; to those who argued and fought for it; to those who designed and built it; and to those who founded and developed its famous company.

"I know it is the determination of the National Theatre Company to fill this building with that special type of magic that only the theatre can provide," she said.

Accompanied by the Duke of Edinburgh, she then watched a performance of Goldoni's comedy Il Campiello.

Laurence Olivier, former director of the National Theatre, after whom the main theatre is named, welcomed visitors with a quote from Henry V.

"It is an outsize pearl of British understatement to say that I am happy to welcome you at this moment in this place," he said.

The National Theatre Company was previously based at the Old Vic in London where it was a resident from 1962.

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