They are the latest allegations to hit Spacey, one of the power players brught down by the cascade of sexual abuse claims roiling Hollywood. 

"The investigation resulted in 20 personal testimonies shared of alleged inappropriate behaviour carried out by Kevin Spacey," the theatre said in a statement.

The allegations cover a period ranging from 1995 to 2013, and the theatre said it was not able to verify any of them.

Spacey became artistic director at The Old Vic in 2004 and stepped down in 2015. 

The theatre said that some of those who made the claims felt they had not been able to come forward and that Spacey "operated without sufficient accountability".

"This is clearly unacceptable and The Old Vic truly apologises for not creating an environment or culture where people felt able to speak freely," it said.

Read also: Spacey dumped by Netflix, police home in on Weinstein

"The investigation found that his stardom and status at The Old Vic may have prevented people, and in particular junior staff or young actors, from feeling that they could speak up or raise a hand for help."

In more than a month since allegations surfaced in the press about serial predatory behaviour by Hollywood producer Harvey Weinstein, victims have said they feel emboldened to voice allegations against men who had been seen as unassailable.

Besides Spacey, a two-time Oscar winner, the blockbuster director Brett Ratner has also been accused of sexual transgressions, while other actors, managers and agents are in the hot seat as well.

The Old Vic said no formal grievances were raised against Spacey during his tenure except for one person who had come forward at the time, and none of the people were minors at the time of the alleged incidents.

It promised a new set of guidelines on inappropriate behaviour, and to establish a new reporting system and provide more guidance and training.

It said its victim support counselling service would be open to anyone "affected" during Spacey's tenure.

"We will foster a safe and supportive environment without prejudice," Nick Clarry, chairman of The Old Vic, said in a statement.

Read also: Spacey hit by new sexual harassment allegations in UK

'A disturbing surprise' 

The theatre's artistic director, Matthew Warchus, said the allegations had been "a shock and a disturbing surprise to many of us" and voiced hope that they would help the industry as a whole.

"It is incorrect, unfair and irresponsible to say that everybody knew. But as a result of the investigation, what we have learnt is how better to call out this behaviour in future," he said.

Spacey is reportedly also being investigated by British police for assault in South London in 2008. 

Scotland Yard said it was looking into a complaint made over an incident in 2008, but the force does not identify people who are subjects of an investigation unless they have been charged.

Spacey is facing a string of abuse claims in the United States, including that he attempted to rape a 15-year-old boy in New York.

A woman in the US state of Massachusetts claimed the "House of Cards" sexually assaulted her 18-year-old son last year, while actor Anthony Rapp accused Spacey of making advances on him when he was 14 years old.

The claims have prompted Netflix to drop Spacey from its popular "House of Cards" series and suspend production of its last and final season. 

The disgraced actor has also been booted from his coming film "All the Money in the World" and replaced by Christopher Plummer just weeks before its release.

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