British police said Thursday they are investigating a man over a third sexual assault, with the Press Association news agency reporting that US actor Kevin Stacey is the suspected assailant.

The assault allegedly occurred in central London in 2005, during Spacey's 11-year tenure at The Old Vic theatre in the British capital.

"On 13 December we received an allegation that the man sexually assaulted a man (Victim 3) in 2005 in Westminster," a Metropolitan Police spokeswoman told AFP on Thursday.

The force does not name people before they are charged with a crime, but the Press Association said the accused was the same man from earlier complaints.

The other two alleged victims said they were assaulted in 2005 and 2008 in the Lambeth area of the city where The Old Vic is located.

They came forward in the wake of the Hollywood scandal which erupted last year after numerous claims of sexual assault and harassment were made against mogul Harvey Weinstein.

Spacey has since faced a series of abuse allegations, prompting The Old Vic to launch an investigation into the actor's tenure at the theatre between 2004 and 2015.

A total of 20 claims of inappropriate behaviour were received, covering a broader period of 1995 to 2013, and have not been verified.