London's Theatre Museum has closed its doors to the public after 20 years because of a lack of funds for a major refurbishment to the building.
Sir Laurence Olivier's costumes are housed at the Theatre Museum
Its owners, the Victoria and Albert Museum, decided to shut the attraction in Covent Garden after failing to raise £5m for the project.
Martin Brown, from performers' union Equity, said he is "appalled" the museum is closing.
Representatives from the Theatre Museum were unavailable to comment.
Mr Brown said: "London is a world-centre of theatre and it's astonishing that the Victoria and Albert Museum hasn't got sufficient commitment to this art form to continue funding a museum."
However, educational activities for groups will continue at the museum building until the end of the current school year, which ends in August 2007.
Sir Laurence Olivier's costume from Richard III and Noel Coward's make-up box are among the exhibits at the museum.
The Victoria and Albert Museum (V&A) plans to rehouse the theatrical collection in a new gallery on its main site in South Kensington.
Other items will be seen on touring displays, education activities and special exhibitions.
The museum has many famous supporters, including actors Dame Judi Dench, Vanessa Redgrave and Peter Bowles.
In March, they wrote a letter to the Times newspaper protesting at plans to close the museum.
They called for "adequate funding" to develop the museum's current site in the heart of theatreland, and "make even more of its outstanding collections available".