What is the story about?
The Daily Mail has been carrying reports for several days about the links between an organisation called the Paedophile Information Exchange and the National Council for Civil Liberties during the 1970s and early 1980s.
It has highlighted the fact that Labour's Deputy Leader Harriet Harman, her husband and fellow Labour MP Jack Dromey and former Labour Health Secretary Patricia Hewitt all worked for the council at various stages.
What was the Paedophile Information Exchange?
It was one of several organisations around the world calling for greater tolerance and paedophile "rights" set up during the 1970s. It campaigned for a lowering of the age of consent to 10 and lobbied MPs for changes to the law.
In 1975 it was granted "affiliate" status by the National Council for Civil Liberties, nowadays called Liberty. This happened before Harriet Harman became the council's legal officer in 1978.
In 1977 the exchange's founder, Tom O'Carroll, gave a speech at the council's spring conference.
The Paedophile Information Exchange and other organisations, such as Paedophile Action for Liberation, said they were basing their call for greater rights on campaigns by the gay liberation movement, which had taken off in the early 1970s.
The exchange was disbanded in 1984, after several prosecutions of leading members and amid press condemnation.
O'Carroll, who served on one of the National Council for Civil Liberties' committees, has told the BBC that Ms Harman, Mr Dromey and Ms Hewitt did not do "much to oppose" its involvement because "their careers in the NCCL depended upon them not rocking the boat too much".
But he says he only met one of the three - Ms Hewitt - on one occasion and that he received no support from any of them.
What was the National Council for Civil Liberties?
Founded in 1934, its stated aim was to defend "the whole spirit of British freedom". Among its many causes, it campaigned against press censorship and internment in Northern Ireland, and in favour of race relations laws and legalising homosexuality. It changed its name to Liberty in 1989.
Liberty's director, Shami Chakrabarti, has called the previous link with the paedophile rights group a "source of continuing disgust and horror".
What does the Daily Mail say?
The newspaper has repeatedly questioned the reasons for the link being established and the role of Harriet Harman, Jack Dromey and Patricia Hewitt in the relationship between the two organisations.
It claims that Ms Harman tried to "water down" child pornography legislation when offering the National Council for Civil Liberties' views on the Protection of Children Bill in 1978.
And what do Harman, Dromey and Hewitt say?
Harriet Harman has insisted her work at the National Council for Civil Liberties was not influenced by the Paedophile Information Exchange and that she was not "apologising for paedophilia or colluding with paedophilia". To say otherwise would be an "an unfair inference and a smear", while her work as a lawyer and politician had been "to protect children, especially from child abuse", she has said.
The Mail was wrong to accuse her of having a "relaxed attitude to paedophilia and of watering down child pornography laws", she has said. Ms Harman has accused the newspaper of pursuing a "politically motivated smear campaign" against Labour.
But she has expressed "regrets" over the links between the National Council for Civil Liberties and the Paedophile Information Exchange.
Jack Dromey has said he made "repeated public condemnations" of the exchange while he worked for the national council, and has said child abuse is "evil".
Patricia Hewitt said the National Council for Civil Liberties was "naive and wrong" over its links with the Paedophile Information Exchange. "I got it wrong on PIE and I apologise for having done so," she said in a statement.
And the Mail's response?
It is calling for Harriet Harman to make an "unreserved apology", saying the statements by her and Jack Dromey are "full of pedantry and obfuscation" and fail to address the newspaper's "central points".
Who is Harriet Harman?
Labour's deputy leader has been an MP since 1982. She joined the National Council for Civil Liberties in 1978 as a legal officer, where she became a noted campaigner for women's rights.
She became social security secretary when Labour took power in 1997 but was sacked in 1998 after a row over welfare reform with another minister, Frank Field. Ms Harman returned to government in 2001 as solicitor general, later becoming a justice minister. In 2007 she was elected Labour's deputy leader.
Who is Jack Dromey?
A long-serving trade union activist, Jack Dromey came to prominence during the strike at the Grunwick photograph-processing plant in west London from 1976 to 1978. He served on the National Council for Civil Liberties' executive committee from 1970 to 1979.
Married to Harriet Harman for more than 30 years, he was elected Labour MP for Birmingham Erdington in 2010 and is a shadow local government minister.
Who is Patricia Hewitt?
Born and raised in Australia, Patricia Hewitt was general secretary of the National Council for Civil Liberties from 1974 to 1983. She later worked for Labour, becoming leader Neil Kinnock's policy co-ordinator. She became an MP in 1997. Ms Hewitt served as health secretary, before standing down when Gordon Brown became prime minister in 2007.
In January 2010, she tried and failed to secure a secret ballot of Labour MPs on Mr Brown's leadership - described as an attempted "coup" by many - and was later suspended by the Parliamentary Labour Party after being secretly filmed by Channel 4's Dispatches offering her services as a lobbyist when she stepped down as an MP. She left Parliament at the 2010 general election.