A Labour MP who has campaigned for an investigation into child abuse rings in the 1970s has taken a swipe at Harriet Harman over the connection between a paedophile rights group and a civil liberties organisation for which she worked.

Tom Watson said he would not have touched the Paedophile Information Exchange (PIE) “with a bargepole”.

Ms Harman, the deputy Labour leader, insists she has nothing to apologise for over the National Council for Civil Liberties (NCCL) giving “affiliate” status to the “vile” group in 1976. But she has expressed “regret” that the organisations were ever linked.

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Tom Watson lamented the fact that the bitter clash between Ms Harman and the Daily Mail, which has accused her of being an “apologist” for paedophilia, had obscured the need to help the PIE’s victims.

But he added that he would never have become involved with an organisation that had any tie with the paedophile group.

“Harriet Harman is perfectly capable of defending herself and doesn’t need me,” Mr Watson told Radio 4’s World at One programme.

“She can explain for herself why PIE ended up being part of that organisation – it’s not something I was involved in. I can just tell you my personal view that I wouldn’t have touched it with a bargepole.”

Mr Watson warned David Cameron in 2012 about the activities of the PIE in the 1970s and 1980s. Theresa May, the Home Secretary, has set up a review into whether the PIE received public money under the Thatcher government.

Nick Clegg said it was a matter for Ms Harman whether she chose to say sorry, but he “strongly supported” an apology from Shami Chakrabarti, the head of Liberty, the successor body to the NCCL.

“She has explained why she has chosen not to apologise," the Deputy Prime Minister said. “She says it was not her decision, the association between this abhorrent organisation and the NCCL.”

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Tom O’Carroll, PIE’s former leader, alleged yesterday that Ms Harman did not try to confront the group because she did not want to harm her career by “rocking the boat too much”.

His claim was greeted with contempt by Ms Harman’s husband, Jack Dromey, who was also an NCCL official at the time. He said no one would believe the words of a convicted paedophile.

It emerged yesterday that O’Carroll sat on an NCCL sub-committee on gay rights in 1979, a year after Ms Harman became its legal officer.

O’Carroll told the BBC that Ms Harman and Patricia Hewitt, the former Labour minister who was the NCCL’s general secretary between 1974 and 1983, had not done much to try to remove the PIE from the sub-committee.

He claimed: “They didn’t do much to oppose PIE’s presence in my view because there were these other liberal forces or radical forces that were in NCCL. The support didn’t come from Harman and co, but it was there.

“The Gay Liberation Front was very radical. At that time Harman and Patricia Hewitt couldn’t just kick out PIE. Well, they could, I suppose, try, but they didn’t even try. And the reason they didn’t try is that they didn’t want to rock the boat because their careers within NCCL depended on them not rocking the boat too much.”

Mr Dromey responded: “It is no surprise that a convicted paedophile, the like of whom I took action against during my time in the NCCL, should choose to smear me.

“The record is clear. I took on PIE and, when I was elected chairman, defeated by a massive majority at the 1976 NCCL annual conference a loathsome motion calling on the NCCL to support the so-called rights of paedophiles.”

Labour sources also said the NCCL at the time was full of subcommittees on which people volunteered to sit rather than were appointed to serve.

The former Cabinet minister Dame Tessa Jowell, a close ally of the deputy Labour leader, said Ms Harman had been “focusing” on work to improve women's rights and to oppose domestic violence during her time at the NCCL.

She said: “There is not one shred of evidence that they [Ms Harman, Mr Dromey and Ms Hewitt] gave any comfort to this revolting organisation.”