Brown's nemesis: Will Paul Moore prove to be PM's downfall?

Paul Moore will go to Mass today, eat Sunday roast with his family, maybe argue a bit with his teenage children, then take his dog for a walk in the fields around his Yorkshire home, five minutes or so from the magnificent grounds of Ampleforth College. "It's magical here," he says: "I can look out of my windows and see across to the monastery where we go for Vespers, listen to the wonderful singing and be calm."

And Moore is astonishingly calm, considering he has just been through the most tumultuous week of his life. For, within a few days, the unknown 50-year-old barrister-cum-banking expert has become the country's celebrity whistleblower. It was his explosive evidence that rocked the Treasury Select Committee's hearing on the banking crisis, leading to the astonishingly rapid resignation of Sir James Crosby, one of the Prime Minister's top advisers and City regulators.

Now, as we reveal today, he wants Gordon Brown to take the rap for his part in creating the credit boom, allowing people to borrow too much, and for letting us go bust. There is more to come. Moore is about to lob his next missile. This week he will be sending some of the more than 30 new documents he has compiled in his time at HBOS to the clerk of the select committee as new evidence, which he says will support his allegations of reckless lending at the bank.

But he never sought to be centre-stage like this. It was only 11 days ago that he even knew there was a Treasury Select Committee being held on the banking crisis, and on the HBOS débâcle specifically. "I read about it in one of the papers last Tuesday and decided within minutes to make my case," he says. "I then sat down, wrote 5,000 words in a day, and sent it to them last Friday morning ahead of the hearing."

No one knew Moore's incendiary evidence was going to be presented because the clerk feared the MPs attending would leak it. "Talk about David running quickly towards Goliath. It's as though a voice told me to go for it," says Moore, a committed Catholic, who helped found the Xt3 Media Catholic social-networking site, and whose classical education peppers his talk with cultural references, from the Homeric legends to St Francis of Assisi.

His ease with the classics comes from just across the fields at Ampleforth, where his father was a pupil and where his three children are today. Basil Hume, the late Archbishop of Westminster, was head of the school when Moore studied there; he recalls skating with Hume over an iced-up lake. "I remember asking him if the rumours that he was going to Westminster were true. He roared with laughter, saying, 'Nonsense.'"

His Roman Catholic faith dictated some serious soul-searching as Moore decided whether to break the gagging order that he had agreed with Sir James, after he was fired by him in 2005. It still haunts him. "I didn't want to do this. I would much rather have forgiven everyone and moved on, so I can understand people who may see me as Judas for having taken the money, and then talking. My answer to that is that I have struggled with this, stayed awake for hours at night, but I have made the decision with integrity. I was completely undecided about taking the money. But when you are a whistleblower you know you might have ruined your career for ever. That's why the damages are relatively high." Moore received more than £500,000 for his silence.

But leaving HBOS devastated him: "I cried when I told my wife I had been fired. But I'll never forget what she said: 'It's God's will and you will find a path.'" Moore met his half-English, half-Colombian wife, Maureen, while hang-gliding in Chile 19 years ago.

Now that "David" is speaking out and running fast, there's no stopping him. Restoring ethics to business is what drives him. Moore joined HBOS in 2002 to head regulatory risk. It wasn't long before alarm bells rang about the heady sales culture. He took his concerns to his superiors, and, ultimately, Sir James, prior to his dismissal. "Look, I love the Halifax, I love the people, and most of the business was good. But there was a terrible culture – created by Sir James – which pushed everybody to try and hit targets that were not possible."

Britain's high debt levels worry him deeply. "You know the adverts that beg you to buy more ? People must be protected from falling into so much debt. This gets to the heart of everything."

He's highly critical of Sir James, whose legacy "will include hundreds of thousands of customers struggling to repay debts they were sold by HBOS, tens of thousands of employees with no jobs, and shareholders whose shares have crashed from £11 to under £1. HBOS is the story of the emperor's new clothes. But anyone who said so wouldn't last."

And now? "There are too many powerful and rich people who have been involved in this mess, and none of them wants an investigation." For Britain overall, he is optimistic that the creative destruction now going on will lead to a healthier and more ethical society.

While he may be bitter over his sacking, Moore is not as critical as you might expect of the regulatory structure, but says there aren't enough quality people to enforce it. The FSA could be transformed with better staff, as fraud goes up in a downturn. Staff such as Moore, perhaps? He laughs, but admits he is returning to mainstream work.

Now that would be divine – whistleblower turned gamekeeper.