John Rentoul: Even now, the impatient Chancellor will not hesitate to strike at Blair if he can

If police charge someone, Brown's dog-handlers will be waiting

Only hours before Ruth Turner was arrested, I was discussing the transition from Tony Blair to Gordon Brown with a former Labour cabinet minister. He was worried the Chancellor might still try to force Blair out of office before he was ready. Surely, I said, after the damage Brown had done to his reputation by the coup attempt last September, he had now called the dogs off. The former minister disagreed. "I know those dog handlers," he said.

So it was that, only hours after the Prime Minister's fixer was arrested, speculation at Westminster turned to whether Brown would be able to use the latest twist in the cash-for-honours inquiry to hurry Blair out of office. I am not, of course, suggesting that the Chancellor instigated the pre-dawn knock on Turner's door at 6.30am on Friday, although Brown's supporters certainly contributed to the forces that launched the police inquiry in the first place.

It is worth recalling the origins of this extraordinary crisis in the attempt to try to understand what might be happening now. It was last March that we found out three Labour donors, whose nominations to the peerage had just been rejected by the scrutiny commission, had lent the party millions to pay for the last election campaign. Three days later, Jack Dromey, party treasurer and husband of Harriet Harman, the Brownite candidate for the deputy leadership, went on television to say he had been kept in the dark about the loans. Six days later Sir Ian Blair, the Metropolitan Police Commissioner, said he would investigate a complaint from a Scottish National Party MP that the obscure 1925 Honours (Prevention of Abuses) Act had been broken. The MP, Angus MacNeil, furnished no evidence, but Sir Ian was fighting for his professional life after a succession of embarrassments, from his handling of the Stockwell shooting to tape recording his phone conversations with the Attorney General. Presumably he feared that if he refused to investigate he would be the subject of further criticism.

It is not at all clear what has happened since then. Despite the complaint of Blair supporters such as David Blunkett about police and Crown Prosecution Service leaks, little has come out.

Whether that is because the police have not found anything substantial, or because they are being discreet, who can say? All we know is that the inquiry has taken a remarkably long time and that the police tactics have been questionable. Few people felt sorry for Des Smith, the head teacher involved in the city academies programme, or Lord Levy or Sir Christopher Evans when they were arrested. Sexism plays its part, as it is assumed they can look after themselves. But a woman at 6.30am? Sexism aside, how could that have been necessary? Police are supposed to arrest people only if they have good reason to think they might disappear or get up to no good. But after four hours they let her go without charge.

By accusing Turner of obstruction - the Scotland Yard statement said she was arrested "on suspicion of perverting the course of justice" - the police raised the stakes. And by saying that they need more time to investigate this "new development" they risk trying the patience even of those who assume the worst about Blair. If they do not charge someone soon, they are going to start looking foolish.

And if they do charge someone, Brown's dog-handlers will be waiting. The idea that the Chancellor is happy to bide his time until July, safe in the knowledge of his certain succession, is a useful fiction. In fact he will be calculating his advantage all the time. If he can get the top job sooner without damaging himself, he will go for it. Even without the cash-for-honours inquiry, there is one final instability that is built into the "stable and orderly transition" that Blair promised. It has taken a while for the penny to drop but, in most organisations, if only one candidate is validly nominated for elected office, they are declared elected as soon as nominations close. If the Labour Party were a normal organisation, Gordon Brown would become leader a mere two weeks after Blair announced his intention to stand down. Two weeks is the time allowed to gather nominations from MPs, and no other candidate is likely to secure the necessary 45. As far as the post of leader is concerned, the four to six weeks required to run a ballot of parliamentarians, party members and trade unionists, could be curtailed.

Fortunately for Blair, the rules are wonderfully unclear on what happens if there is only one candidate (not least because it has never happened before). Hence the plan for an "affirmative ballot" to endorse Brown, run in parallel with the deputy leadership election. But I am told by a well-placed source that this is a non-starter, on the persuasive grounds of its similarity to North Korean arrangements.

In order to spin out the process, the Prime Minister is going to have to rely instead on the provision in the rules for constituency Labour parties and trade unions to provide "supporting nominations" for candidates. So we are likely to be treated to the curious spectacle of Blair, still Prime Minister, and Brown, already in effect Labour leader, presiding over a deputy leadership election in which Jon Cruddas, the anti-leadership candidate, does surprisingly well.

Yet what else might be in store? Brown is the world's greatest authority on cups, lips and all that is betwixt and between. He thought the top job was his in 2004, yet Blair defied a heart operation, the opponents of the Iraq war and political gravity to survive until now.

I thought that Brown seemed more relaxed since Christmas, and assumed that, because rich and important people were already looking to him to make decisions in advance of his taking office, he was already enjoying the confidence of power. His TV interviews have taken on a sort of Zen Prescottian quality, where the transcript loses all semblance of syntax but it is perfectly clear what he is saying. And at the Fabian Society last weekend he even took questions from the audience. He was not great at it but he came across much better than he did in his prepared speech.

I should not have been fooled. The idea of Brown reconciled to waiting has not been true for 13 years, and it is not true now. Ruth Turner's arrest was a reminder that stuff happens in politics, and if Brown can take advantage of events to cut Blair short, he will.

The dogs are still straining at the leash. The Blair-Brown faction fight is not over yet.