John Rentoul: Tony Blair and the Richly Fellows: the final chapter

Spoiler warning: if you do not want to know the ending of the latest Harry Potter book, look away now. Very few people have noticed this sinister apparent coincidence. The first Harry Potter book was published in June 1997, the month after Tony Blair became Prime Minister. The last Harry Potter book has been published the month after he ceased to be Prime Minister.

But if Blair is Potter, then who is Voldemort? All along, for six books and 10 years, we thought it was Gordon Brown. But now comes the twist, the surprise ending at which J K Rowling excels, in which we find out that Blair's arch enemy was someone else entirely. Of course, Brown was a great enemy, and he played his part in the intricate plot of the seventh and final instalment of the story, Tony Blair and the Richly Fellows.

It was one of Brown's outriders, Jack Dromey, who detonated a cash-for-honours bomb in March last year by going on television to say that, as Labour Party treasurer, he had not known of the £14m in secret loans that funded the 2005 election campaign. As Charles Clarke commented acidly at the time, he wasn't much of a treasurer if he hadn't asked where this substantial largesse was coming from. But this was politics, not double-entry bookkeeping, and now he has been rewarded for causing trouble for Blair. His wife, Harriet Harman, sits at Brown's right hand, elected deputy leader of the party by a narrow margin with the backing of several notable Brownites.

Dromey's intervention helped to create the climate in which Sir Ian Blair, the Metropolitan Police commissioner, took the extraordinary decision at the heart of this story: to order an investigation into the alleged sale of peerages.

However, neither Dromey nor Brown – if he had even known what his freelance knight was up to – could have predicted that Sir Ian would have responded as he did to an opportunist letter from Angus MacNeil, the Scottish National Party MP. As a plot device, the whole thing required an implausible series of coincidences. There was Dromey, engaged in internal Labour politics; MacNeil, engaged in inter-party politics; and there was Sir Ian, in deep trouble only three days earlier, having to apologise to the Attorney General and to the head of the Independent Police Complaints Commission for tape-recording their phone-calls about the inquiry into the Stockwell shooting.

And off the story went, gathering up the strands that had been cleverly woven into the earlier parts of the narrative. There was the ancient prehistory of Lloyd George and Maundy Gregory (a made-up Rowling name if ever there were one). And there was the recent history, repeating itself if not as farce at least with a heavy sense of irony, of the Blair government's legislation for disclosure of party funding.

The story was driven on by misunderstandings that were more Thomas Hardy than Rowling. John Yates, the self-important policeman, could hardly look at MacNeil's complaint and say: "Nothing in it, sir, just a cut-and-paste job from The Sunday Times." Then there really would have been howls of "whitewash!". So he arrested the headteacher who had been stung by The Sunday Times into saying that someone who gave £10m to academy schools would be "a certainty, almost", to be nominated for a peerage. It was only then that Yates realised what should have been obvious: that this was a prediction not a promise.

By now the story had taken on a life of its own. Just as Voldemort initially had no body and had to live a parasitic existence, so Blair's enemy gathered its strength until it became a self-sustaining organism. This was greater than the feral beast of the media of which Blair spoke in his last main speech as Prime Minister – "a feral beast, just tearing people and reputations to bits" – although many media outlets provided host bodies.

These included The Times, which on 5 February this year quoted "a prosecution source" who would be "very surprised" if Lord Levy, Ruth Turner and Sir Christopher Evans were not charged. And The Sunday Times, which on 11 March said the police were "confident of charging Levy with breaching the 1925 Honours Act, which bars the sale of honours, and with perverting the course of justice".

More alarmingly, the organism engulfed the BBC, which at one point offered its staff a cash incentive – £100 of public money – for a "new angle" on the cash-for-honours story.

"Has Tony Blair besmirched the office of prime minister?" screamed the impartial Kirsty Wark on Newsnight on the day he was interviewed by the police. (It is an iron rule that a question in a headline is a mistake because the answer is always "No", but it is not a rule that excuses BBC bias.)

Partly driven by the desperation of journalists for the allegations to be true, the police ploughed on, covering their backs with the Crown Prosecution Service every step of the way.

Blair has clearly decided not to criticise the police tactics. He and his aides, Turner and John McTernan, said that the police were just doing their job. Even Lord Levy, who expressed his fury at being arrested at the time, was reduced last week to an expression of "disappointment" about "constant leaks to media". But why was it necessary to arrest Levy and Sir Christopher Evans when they turned up at police stations for pre-arranged meetings, when police guidelines say that "officers exercising the power [of arrest] should consider if the necessary objectives can be met by other, less intrusive means"?

So who was really behind the unlikely alliance of Gordon Brown supporters, Metropolitan Police commissioners and the feral beast that helped to force Blair out of office prematurely?

Here the great storyteller springs her surprise, because none of this would have happened if Blair himself had not taken such reckless risks. First he took secret loans to pay for his last hurrah on the hustings. Then he took the even more extraordinary risk of trying to nominate four of the lenders to the peerage while trying to keep their loans secret. Never mind the allegations – for which there never was any evidence – that the law had been broken. The police investigation was a distraction. But while it was unfair and wrong that Blair's reputation should have been damaged by a criminal investigation that should never have been launched, his reputation should have been damaged.

What we know for a fact that Blair tried to do was reprehensible enough. Of course, it was no worse than what previous prime ministers did: rewarding donors without giving them the certainty of a bill of sale.

But Blair had held himself out as better than that and had legislated for openness. And so the story turns out to be an old-fashioned morality tale: he brought it on himself. Voldemort was his own creation.

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