The 58-year-old actor, who is also charged with downloading child pornography, denied having a lust for young girls, Maidstone Crown Court heard.
Langham claimed his alleged victim, who is now 25, jokingly told him that she wanted to kill his children and had violent fantasies about him punching her in the face.
Prosecutor Richard Barraclough QC suggested Langham was “prepared to torture her by making outrageous allegations against her”.
Langham said: “She’s a sick person, I’ve never made any allegations against her.
“I mean that in a completely compassionate way. It’s not a criticism or judgment. I can’t say I like her very much but everybody deserves compassion.”
The jury has heard he gave acting lessons to the woman in his dressing room when he was starring in Les Miserables in London’s West End. She claims she lost her virginity to him shortly afterwards in a London hotel.
The actor revealed that his arrest on child porn charges in November 2005 had troubled the woman.
He said: “She was very upset by the charges and she said she thought I was guilty. She wanted to know if my relationship with her was not affected by a sexual interest in children.”
The actor said she was also worried that “I was looking at her in that way” and said: “I was able to say that I wasn’t.”
Mr Barraclough said: “Were you frightened that this girl was going to go to the police and complain about the sexual activity you’d had with her as a child?”
“No,” Langham replied.
He was arrested 10 months later for allegedly having underage sex with her. The actor said it was a “terrifying” experience.
Langham, of Golford, near Cranbrook in Kent, denies 15 counts of making an indecent photograph of a child between September and November 2005.
He also denies six counts of indecent assault and two counts of buggery between January 1996 and April 2000.
Four further counts of indecent assault were dropped after the Crown accepted there was no evidence to support them.