James Harkess, whose wife and two step-daughters were seduced by the former defence minister, is on a "moral mission" to canvass for Mr Clark's Labour opponent.
Mr Harkess, a barrister and former judge, has flown half way round the world to campaign on behalf of Robert Atkinson, the Labour Party candidate in Kensington and Chelsea. He is, he says, sick of Tory "sleaze".
The last time Mr Harkess came to Britain from his home in South Africa was in May 1994 when he told the News of the World that Mr Clark deserved to be "horsewhipped" for having a simultaneous affair with his wife and her daughters Alison, 39, and Josephine, 37. In his memoirs, Mr Clark described the three women as the "coven".
This time he is spreading his message door-to-door. He has already been out canvassing with 91-year-old Lord Longford and intends to join Mr Atkinson regularly in the run-up to the general election. His wife, Valerie, 59, was due to join him in Britain yesterday.
"Clark is a man unsuitable for politics," said Mr Harkess. "It's his dishonesty as well as his sexual peccadilloes," he added. "I think I should be able to say what I believe and try to stop that which is ugly, dishonest and wrong."
Although he briefly supported the Labour Party as a teenager, Mr Harkess, 67, has otherwise been a lifelong Tory. He even stood as a Conservative candidate for Brixton in south London in the 1970 election, declaring himself a supporter of Enoch Powell's position on immigration.
Mr Harkess denies that he is wreaking revenge on his old rival. "This is nothing to do with any vendetta or anything of that kind," he said. "I don't believe in vendettas. I have forgiven Alan Clark."
He added: "That doesn't mean that I don't have a right and a duty like everyone else to say what I think is right and what I think is wrong. And one of the things I think is very right - and I want to be positive not negative - is what Tony Blair is doing in the next two weeks in order to become Prime Minister of this country."
He is, he says, disgusted with the Conservative Party. "It's the whole question of trust, honesty and leadership, and of course, moral and family values," he said, claiming there were about 30 Conservatives who "could be labelled sleaze candidates".
"What is bringing the election down is that there is too much sleaze going on in the Conservative Party," he said. "There is something very wrong with the state of the country when the Prime Minister cannot do anything about that and put it right."
Mr Clark said yesterday: "He [Harkess] says he has forgiven me. Well, that's very generous of him and very Christian of him. I have expressed contrition the last time this was raised four years ago and the episode is 20 years old.
"I don't like talking about it. It's very, very old. It really is historic and I am trying to fight an election now."Reuse content