An alleged sex assault victim of Kevin Spacey said the "slippery" Hollywood actor had tried to "groom" him before later repeatedly groping him, a London court heard on Monday.

Spacey, 63, is on trial at Southwark Crown Court accused of a dozen allegations of historic sex offences committed against four men, then aged in their 20s and 30s, which are said to have taken place between 2001 and 2013.

He has denied all the charges and his lawyer said last week at the start of the trial the jury were going to hear some "damned lies".

On Monday, the court was shown a recorded police interview with the first of the alleged victims. The man said the actor had assaulted him on up to 12 occasions over a period of about four years in the early 2000s, grabbing his "private areas" when they were alone, such as in a car or an elevator.

After two to three weeks of being with Spacey, the actor had begun rubbing the man's legs and neck while he was driving, before later starting to grope him or force the man's hand onto his genitalia, he said.

"He was almost, from the get go, grooming me," the man said in the interview.

The alleged victim, who cannot be identified, said the "touchy feely" actor had on one occasion aggressively grabbed his crotch so hard when he was driving him to a party hosted by singer Elton John that he almost crashed the car.

Describing himself a "man's man", the accuser recounted that he had threatened to knock the actor out if he did it again, to which Spacey had replied "that's such a turn on to me".

He described Spacey as a "slippery", difficult person, a "mixed-up individual" who was very confused about his sexuality. The man said Spacey's behaviour was an open secret at the London Old Vic theatre where he worked for more than a decade.

"It was well-known that he was obviously up to no good so to speak," the man said.

The trial is due to last about four weeks.