Britain’s leading fathers’ rights charity is in turmoil after it emerged that one of its senior figures used the organisation to influence a child custody hearing against a father, The Times has learnt.

Families Need Fathers (FNF) is to pay tens of thousands of pounds in damages and legal costs after one of its officials admitted writing a defamatory letter to a judge in an attempt to undermine the father’s custody case.

Steve Stephenson, FNF’s London branch organiser, admitted that he should not have made the “false and defamatory allegations”, which were vetted by the head office of the government-funded charity.

The case has highlighted the secrecy in which the family justice system is shrouded, because the father – who cannot be named for legal reasons – was unaware of the allegations against him for several months.

It was only when the father, a working professional in his fifties, requested correspondence from his file that it came to his attention and he refuted the allegations. Three court hearings had taken place in the meantime.

News of Mr Stephenson’s intervention, which was written on an FNF letterhead and incorrectly alleged that the court had been deceived by the father, ignited a fierce reaction. On an online forum for FNF members one wrote: “Does anyone know why he would represent something detrimental to children and against FNF’s main aim? Has he lost the plot?”

The charity receives a government grant of more than £300,000 a year and David Blunkett, the former Home Secretary, is one of its patrons. Bob Geldof is also a supporter.

Mr Stephenson wrote the letter in July last year. He was assisting the ex-wife in the hearing by acting as her “McKenzie Friend” – an aide for litigants without legal representation.

The father said: “FNF’s role in this matter is especially surprising because it is an organisation that campaigns against injustices in the family courts.”

Jon Davies, the chief executive officer of FNF, said that a mistake had been made and an apology made. He said new policies had beeen drawn up, and distributed to all staff and officers within FNF, to ensure that such actions were not repeated.

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