Beckham has already dismissed as ludicrous claims from Rebecca Loos that she had sex with the 28-year-old midfielder in Madrid.

Beckham and his pop star wife Victoria called in lawyers after a Sunday newspaper printed allegations from a second woman -- 29-year-old Sarah Marbeck -- who said she had an affair with Beckham.

But Loos, the 26-year-old daughter of a Dutch diplomat, insisted in a television interview being screened on Thursday night that she was telling the truth and could prove it.

"There's something I know about him, an intimate part of his body that I think only women who have been in bed with him would know," she told Sky One in the interview.

"So I think if they did want to take me to court, I could easily stand up and say, 'Well' ...."

When asked if Beckham was circumcised, Loos said: "I'm not going into that. I'm not talking about that. If I do ever need to talk about that, it'll be in a court, not on TV."

A spokesman for Sky One told Reuters: "We have received a legal letter from David Beckham regarding the interview. We cannot go into details. We are still on course. The program has not been suspended though the content is still being finalized."

Britain's tabloid press, who have gone into a feeding frenzy over the claims, gave blanket coverage to Loos again on Thursday. Bookmakers even offered odds on what the intimate detail might be -- from tattooed buttocks to a spotty back.

Loos' latest claims were splashed over the Sun, Britain's leading tabloid which, along with Sky Television, is part of the global media empire owned by Rupert Murdoch.

In the interview, Loos shows off raunchy text messages that she said she received from Beckham, a British sporting and fashion icon famed for his squeaky clean image as a devoted family man.

She also said Beckham fed her strawberries at breakfast in a Madrid hotel bedroom and made her feel "like a million dollars."

Insisting her story was 100 percent true, she said: "There is no doubt in my mind. I have no reason to lie. Why should I? I was wrong to have done what I did. But it did happen and I'm not going to live a lie for the rest of my life."

Meanwhile, Malaysian-born Marbeck from Australia, was alleged by The Sun newspaper to be a call girl.

The tabloid claimed she joined Sydney's exclusive Boardroom Escorts' Agency after she says she slept with Beckham.

The agency confirmed the Malaysian-born Marbeck worked for the company in 2001 but declined to comment any further.

The Sun said Marbeck worked for the exclusive Boardroom Escorts Agency six months after the second of her alleged romps with Beckham.

The Boardroom Escorts boss Graeme Edwards told The Sun Marbeck visited clients in their hotel rooms.

Beckham and his Real Madrid team-mates were forced out of the Spanish capital on Wednesday after fans protested about reported bad behaviour by the players.

"For you, whores and money, for us, indignation and repression" was the banner which greeted the Real players when they turned up for training.

Real, dumped out of the Champions League 3-1 by Monaco, crashed 3-0 at home to Osasuna in their first home defeat in the Spanish league last weekend.

And on Wednesday, the squad left Madrid for a secluded training camp in the south of Spain