Fiona Woolf has resigned as head of an inquiry into historical child sex abuse after mounting pressure that she was unsuitable for the role because of her links to Lord Brittan.

The ceremonial Lord Mayor of London had been heavily criticised over her links to former Home Secretary Lord Brittan, whose role is expected to come under scrutiny in the investigation.

Woolf had faced calls to step down from her role investigating abuse from victims' groups.

The groups questioned links between Woolf and Brittan who was home secretary in 1984, when ministers were handed a dossier listing alleged high-profile paedophiles.

Brittan was expected to be hauled in front of the inquiry after it emerged documents relating to alleged paedophilia in Westminster disappeared from his department. He denies failing to act on the dossier while in office in the '80s.

"If the victims weren't confident then I was getting in the way," Woolf told the BBC. "I needed to get out the way, the victims have to be heard."

Home Secretary Theresa May issued a statement saying she "regrettably accepted" Woolf's decision.

"I believe she would have carried out her duties with integrity, impartiality and to the highest standard," she said in a statement.

Woolf becomes the second person to resign from leading the inquiry after Lady Butler-Sloss stepped down because her late brother, Lord Havers, was attorney-general during the period in question.

Prime Minister David Cameron had been "absolutely clear" that she could do the job, a Number 10 spokesman said.

A letter from Woolf about her links with Lord Brittan was re-written seven times. Asked about whether redrafting the letter with the help of the Home Office undermined how impartial she appeared, she said: "It does look like that."

Home affairs select committee chairman Keith Vaz said: "It needs to be third time lucky for the home secretary."

Former Home Secretary Sir Leon Brittan
Lord Brittan has issued statement on paedophile dossier, denying it was supressed. Reuters