Before former UK prime minister Gordon Brown sent a draft of a scathing comment piece on the Jeffrey Epstein scandal to The Guardian earlier this month for publication, he asked friends whether he had gone too far.

He 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”.

Those whose counsel Brown had sought over the piece reassured him he was right to use the strongest terms.

Mandelson, the de-facto deputy prime minister in Brown’s government, was arrested on Monday on suspicion of misconduct in public office. He denies any wrongdoing.

Brown’s dogged pursuit of the documents relating to the Epstein scandal, before and after the Guardian article, has drawn comparisons with that of the hangdog Scottish detective Jim Taggart of the eponymous crime series.

When the first Epstein emails emerged last September, suggesting an unknown level of closeness between Mandelson and Epstein, Brown wrote to the then British cabinet secretary, Chris Wormald.

He sought correspondence relating to the former cabinet minister’s communications with Epstein. Brown was informed no such papers had been found.

In a piece published by the New Statesman six days after his Guardian article, Brown turned his clunking fist, as Tony Blair once described it, on the alleged predators and enablers.

“In the past week, I have delved deep into the Epstein files,” he wrote. “What I discovered about the abuse of women by male predators and their enablers – and Britain’s as yet unacknowledged role – has shocked me to the core.”

Brown reported that “a number of British girls were on 90 Epstein flights organised from UK airports on what was called his ‘Lolita Express’” and alleged “Epstein was able to use Stansted airport – he boasted how cheap the airport charges were compared with Paris – to fly in girls from Latvia, Lithuania and Russia”.

Brown said that, in his view, police should speak to Andrew Mountbatten-Windsor about what he might know, if anything.

Brown sent a five-page memorandum of evidence to six police forces that cover airports used by Epstein. On February 19th – the former prince’s 66th birthday – Mountbatten-Windsor was arrested on suspicion of misconduct in public office. He also denies any wrongdoing.

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

Rewcastle is married to Brown’s brother Andrew. “Quite a lot of people have been turning to him with information,” she said. “I have been dragged into doing some of the background work.”

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

Speaking anonymously, those who have known Brown for a long time do not doubt this but suggest it is not quite the full picture. It is complicated, they say; Brown is complicated.

“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.”

According to one source, when Brown decided to invite Mandelson into his government from Brussels, where he had been European commissioner for trade, the plan had been for him to be made deputy prime minister.

This fell foul of senior figures – “mainly those who also wanted to be deputy prime minister”, a source said – and so the title given to Mandelson in 2009 was first secretary of state.

Brown is said to have been advised by a close ally that it was a “very significant risk and not worth taking” but the decision to bring him back, kept to a tight circle, had already been taken.

A source close to Brown countered that it was part of a wider move to bring in economic expertise, including the city grandee Paul Myners, at a time of financial crisis. Brown had even called the then European Commission president, José Manuel Barroso, to find out if there was any reason not to execute the move, the source added.

Mandelson joined the education secretary and former UK treasury adviser Ed Balls in an inner circle that would meet on a Sunday night in Downing Street for “fireside chats”.

The response to the Epstein revelations among Labour MPs is said to have been one of anger while that of the parliamentary party in the Lords is of grief, given the sense of betrayal by one of their own, said a party insider.

“But for all the personal betrayal, Gordon is firmly in the anger camp,” said the source. “He is profoundly, almost to the point of annoyingly, moral. During the expenses scandal, one of the chief whips said of Gordon that he had never met anyone less interested in money.”

Brown’s stubborn, activist-like use of this anger over the Epstein scandal was said by insiders to be simply part and parcel of who he is.

Brown’s aversion to going on holiday when he was chancellor and then prime minister was depicted while in government as a consequence of his devotion to public service but “he also just doesn’t like going on holiday because he would rather sit in his house probably still wearing a suit writing press releases that would never be sent”, said a source. “Raith Rovers will only take up so much of the day,” the source added of the football team Brown supports.

While Brown would erupt with fury at critical articles offering well-intentioned advice when he was in No 10, now he is a constant source of advice, to the mild irritation of some within government.

The causes taken up by Brown in his post-prime ministerial career have ranged from seeking a fresh police investigation into Rupert Murdoch’s company’s alleged cover-up of phone hacking – it denied wrongdoing – to the reversal of the two-child benefits cap and the need for improved palliative care before legislation is passed on assisted dying.

“It is like Ted Heath on steroids,” said one Labour source. “But on the Epstein stuff he is right – he is driving this and clearly making the weather.”

For now, Brown is understood to be happy to let the police investigations take their course. He has a new book out in September on global politics. Next week he will seek to publicise a new VAT relief that effectively scraps the requirement for businesses to pay VAT when donating goods to charity.

It is a policy that Brown hopes will assist, among others, Multibank, a charity he started in Kirkcaldy that distributes products donated by businesses to disadvantaged families. “Gordon sees everything as a moral crusade,” a source said, “and when it’s good that fire is amazing.” – The Guardian