Insisting that she was in no way responsible for the story reaching the press, she said: 'I'm being made to look like a tart strutting her stuff for all to see. It is grotesque. I have never done anything at all that I am ashamed of.
'I feel I am the victim. I shouldn't have to. But I have kept my self-respect and I will rebuild my life,' she said.
Speaking as Downing Street indicated that an increasingly embattled Mr Mellor had the full support of the Prime Minister, Ms de Sancha accused newspapers of printing lies about her life and her role in the alleged affair.
Speaking at a hotel outside London, the 31-year-old actress, who was dressed elegantly, appeared close to tears during the interview. In the mannered tones of a professional actress, she denied that she had been paid to reveal the affair to the People, which broke the story last Sunday and carried the transcript of a tape-recorded conversation with Mr Mellor, Secretary of State for National Heritage.
She said that she had 'reason to believe' that her telephone had been tapped but added it was 'a complete and utter mystery to me' how the press had obtained the tape or the transcript.
Press reports have named her former landlord Nick Philp, the 'electronics expert' who rented her a room in his house in Chelsea, as being involved in the leaking of the story, but she refused to talk about him.
She denied selling her story: 'I would never stoop so low as to do anything to get money in this situation. Do people really think I would do anything that would lead to being treated like this by the press? I cannot go out. I feel like the Elephant Woman.'
Ms de Sancha said that a privacy law should be brought in to protect people like herself. 'There has to be a law and it has to be abided by. People have told the most terrible untruths about me. Papers should be prevented from printing those stories.'
She said that she was considering taking legal action against them, and going to the Press Complaints Commission, which said yesterday that Mr Mellor had made no formal complaint about press coverage.
Ms de Sancha would not comment on whether David Mellor was the best politician to consider the issue of privacy, nor would she talk about their relationship. Peter Meineck, of the theatrical production company Aquila Productions, a former employer who is acting for her, said she had agreed to talk to the Independent as a 'damage limitation exercise' and had no desire to inflame the situation.
But she said there were almost no cases where a person's private life was relevant to their professional business. 'As long as it doesn't affect what goes on in your professional life it doesn't matter at all. Your professional life is your professional life. They are two separate issues. We are all human beings. I don't think it is the public's business, I don't think they have a right to know.'
Since the scandal broke, the public has been offered many lurid stories about her. The Sun revealed she had acted last year in what it described as a 'soft-porn' film called The Pieman and carried a number of pictures of her semi-clothed and engaged in simulated sex acts. It printed an interview with Dominic Prince, a journalist who claimed to be a former lover, under the headline 'She gave a great toe job'.
The Daily Express called her 'selfish, self-obsessed, neurotic and high-handed'. The Daily Mirror printed a picture of her bedroom under the headline 'How could he sink so low?'
Topless promotional pictures of Ms de Sancha have been printed without her permission, and many papers have run photographs of her scantily clad at parties. She said: 'I'm very shocked at the whole thing, I'm devastated. These are outrageous and appalling, out-and-out lies that are being printed about me. 'People are being quoted as my friends who I've never met. I'm trying to be very strong. But I would rather have been hit over the head than go through this.'
Ms de Sancha - who trained at Rada and has acted in several classical plays - said she was a serious actress who wanted to work at her craft. The Pieman was 'a short film, and yes, there was a bed scene. Well so what? It was not a porn film, it was a perfectly clean normal film, nothing wrong and my clothes remained on.
'Many classical actresses have played bed scenes, look at Glenda Jackson. It's part of life. As long as it's all in good taste, I see nothing wrong with it.'
She expressed disbelief that the media had 'wasted so much time on this story . . . There are so many more important things. People fighting, being murdered. Let's face it, there's a real world out there. Can we please do something about it because it's really important.'
Major backs Mellor, page 2
Letters, page 20
Last chance saloon, page 21