Former Labour Health Secretary Patricia Hewitt has apologised for having "got it wrong" in the row over a pro-paedophile group.
She said she took responsibility for mistakes made by the National Council for Civil Liberties in the 1970s when she was its general secretary.
The NCCL was "naive" over its links with the Paedophile Information Exchange (PIE), Ms Hewitt said.
But she had never condoned the "vile crimes" of paedophiles, she added.
It is the first time Ms Hewitt, who said she had been away for the past 12 days, has publicly spoken since the latest controversy broke.
She said more should have been done to protect the integrity of the NCCL from the activities of PIE, which was allowed to join the organisation as an affiliate member in 1975.
In a statement, Ms Hewitt explained she had only been able to study allegations made by the Daily Mail upon her return to the UK and said: "Any suggestion that I supported or condoned the vile crimes of child abusers is completely untrue."
The newspaper has questioned Ms Hewitt, along with deputy Labour leader Harriet Harman and Ms Harman's husband and fellow Labour MP Jack Dromey, over their actions while officials at the NCCL in the 1970s and 1980s.
Ms Hewitt said: "NCCL in the 1970s, along with many others, was naive and wrong to accept PIE's claim to be a 'campaigning and counselling organisation' that 'does not promote unlawful acts'.
"As general secretary then, I take responsibility for the mistakes we made. I got it wrong on PIE and I apologise for having done so.
"I should have urged the executive committee to take stronger measures to protect NCCL's integrity from the activities of PIE members and sympathisers and I deeply regret not having done so."
Ms Hewitt said that in particular, PIE member Tom O'Carroll - who was convicted of child pornography offences in 2006 - should not have been allowed to join the NCCL's gay rights sub-committee.
A proposal by the NCCL to lower the age of consent was not made by her but was the policy of the organisation and its executive committee, she added.
Ms Hewitt, who was general secretary of NCCL from 1974 to 1983, said: "I do not support reducing the age of consent or legalising incest."
Ms Harman has accused the Daily Mail of "smear and innuendo".
While she said she "regrets" that the NCCL had links to PIE, she has insisted that she has nothing to apologise for.
Mr Dromey has insisted that he made "repeated public condemnations" of the pro-paedophile group.
Speaking on BBC One's Question Time, Conservative defence minister Anna Soubry said: "I think Harriet has handled [the story] very badly. If she had just come out and apologised, it would have gone away."
She added: "I don't think she has done herself any favours. Neither has Jack Dromey."
But, for Labour, shadow education minister Rushanara Ali said: "Harriet has spent a lifetime campaigning for women and children. The idea that she would campaign for paedophiles is wrong and ludicrous."
She also said: "There's an argument that the Daily Mail has got an agenda against certain senior figures in the Labour Party."
And Plaid Cymru's Westminster leader, Elfyn Llwyd, said it was wrong to criticise Ms Harman, who had joined the NCCL in 1978, more than two years after the affiliation with PIE was agreed, and had been a "junior lawyer".
"Asking her to apologise is like asking me to apologise for the First World War," he said.