I've played with Mosley so much I know how far to push him, says S&M mistress

Enduring 12 strokes of the birch, or administering them to a sexual partner, creates the "best feeling in the world", according to the woman who organised sado-masochistic sex sessions for the motorsport boss, Max Mosley.

The woman, identified in court only as A, was giving evidence on the second day of the High Court trial in London in which Mr Mosley is suing the News of the World for invasion of privacy and defamation after it published articles, photographs and video footage showing Mr Mosley engaged in sado-masochistic role play.

The woman was asked by David Sherborne, representing Mr Mosley, whether she agreed with the newspaper's description of the S&M sex sessions as "grotesque" and "brutal". She replied: "For us, they're certainly not grotesque. Brutal – definitely not. It's consenting adults and because I've played with him so much I know how much I can push him. You set yourself a certain level – 12 cane strokes – and once that number has been set you want to get there.

"It's like being in a competition. You want to win the race. It's the feeling you get afterwards – it's the best feeling in the world."

She also compared it with the "challenge" of running a marathon, and said that the adults involved in these sessions are "like children playing cowboys and indians".

Mr Mosley has admitted paying five women £500 each to join in a "party" that involved military jackets and caps, striped prisoners' uniforms and beatings. During part of the session, he and a German woman – woman B – pretended to be prison guards, speaking in German and dealing out "punishment" to women who posed as prisoners.

The session was described by the News of the World as a "sick Nazi orgy", but Mr Mosley denies it had any Nazi theme. "Had I wanted a Nazi scene, I would have said I wanted one and A would have got some of the inexpensive Nazi stuff from the joke shop that provides uniforms and would not have gone to Marks & Spencer and got quite expensive jackets," he said.

Woman B, speaking with a strong German accent, said she was wearing a Luftwaffe jacket that she had bought years earlier in Camden Market, together with a suspender belt, stockings and black patent leather high-heeled shoes. But she too denied that the scene had any Nazi connotations.

"It is an insult and offence if a newspaper equates German with being Nazi – my grandparents were not members of that party," she said. "It makes me so cross and angry."

Mr Mosley said speaking German had added to the excitement of the sexual role play. "German also somehow sounds appropriate for a bossy, dominant character. It is a harsh-sounding, rather than a romantic, language," he said.

He also complained that the News of the World report on 30 March "destroyed my entire life and that of my family". But the women involved, whose identities are protected by a court order, appeared to be enjoying the day, to the extent that Mark Warby QC, representing the News of the World, called them "a giggling gaggle."

When Mr Sherborne produced as an exhibit a prisoner costume used in the sex session, A burst into laughter in the witness box and told him: "It suits you." She then apologised to the judge for her levity.

Another of the women, D, also laughed as she gave evidence about the pleasures of sado-masochistic sex. "It's something I enjoy and I don't see why I shouldn't practice it in my own personal space," she said.

Asked whether it was painful, she replied: "Yes, but in a good way – painful but not excruciating. I would rather be doing CP (corporal punishment) a long way over going to the dentist."

Mr Mosley also said that in January he was warned by the Formula One boss, Bernie Ecclestone, that a rival within the sport was having him investigated. On 26 February he had lunch with Sir John Stevens, the former head of the Metropolitan Police, who warned him: "You should be very careful, because you are being investigated."

Mr Mosley then added: "Either it was simply a coincidence and the News of the World stumbled on it, or the people who were investigating me... tipped off woman E," he said.

Mosley, M&S and S&M

* "Had I wanted a Nazi scene, I would have said I wanted one and A would have got some of the inexpensive Nazi stuff from the joke shop, and would not have gone to Marks & Spencer and got quite expensive jackets."

* "A Nazi theme would be abhorrent to me – and I suspect that none of the women would wish to take part."

* "All my life, I have had hanging over me my antecedents, my parents, and the last thing I want to do in some sexual context is be reminded of it."

* On an episode in the role-play involving checking for nits: It was "the kind of thing these people do all the time. I had never had lice-checking before but went with the flow. I didn't find it particularly erotic".

* "I fundamentally disagree with the suggestion that any of this is depraved, fundamentally disagree with the fact that it is immoral. I think it is a perfectly harmless activity provided it is between consenting adults who want to do it, are of sound mind, and it is in private."