Before Gordon Brown sent a draft of his 6 February comment piece on the Jeffrey Epstein scandal to the Guardian for publication, he asked friends whether he had gone too far.

The former prime minister had written that he found it “hard to find words to express my revulsion at what has been uncovered about Epstein and his impact on our politics” and the “time is overdue to let in the light”.

On Peter Mandelson’s alleged leaking of market-sensitive documents to the disgraced financier and sex offender during the financial crisis, Brown was particularly vexed.

If it had happened, he said it would be, in his view, “a betrayal of everything we stand for as a country”.

Brown is said to have been searching through the Epstein documents himself but he has also been assisted by Clare Rewcastle, a journalist whose past investigations have included exposing corruption at the Malaysian sovereign wealth fund.

Asked about Brown’s motivation, Renwick said it should be taken at face value: he had been utterly appalled by Britain’s apparent role in enabling a web of exploitation.

"He might not even be conscious of it or acknowledge it but he will feel guilty,” said a Labour insider. “He was the person who brought Mandelson back in the house.”