Dominic Lawson: Mr Yates is answerable only to the law

Through charm and political force, Blair has always managed to impose his will on the legal system

The relationship between the Home Secretary and New Scotland Yard is never an easy one; but it's safe to say that David Blunkett came to be held in greater contempt by the Yard than any other modern holder of that office. His tantrums were one thing - he was by no means the only cabinet minister to be a shit; but when he leaked to the editor of the Sun details of what he regarded as blunders by the then Metropolitan Commissioner, John Stevens, he was marked down as a treacherous shit.

Now that Mr Blunkett's links with Britain's most demotic newspaper are official - he writes a weekly column for the Sun - it was no surprise to see him appearing in its pages as a critic of the Met's arrest at 6.30am last Friday of Ruth Turner, Tony Blair's Downing Street "gatekeeper". "We want thoroughness not theatre," declared Mr Blunkett, adding that "the Metropolitan Police [should be able] to distinguish between a criminal likely to avoid capture and a woman doing a decent job on behalf of the Prime Minister."

I am not aware of Mr Blunkett having accused the Met of theatrics on any of the countless previous occasions when it has arrested somebody at an even more unsocial hour.

More to the point, Ms Turner was being arrested on suspicion of perverting the course of justice; specifically, the "cash-for-peerages" team of Deputy Assistant Commissioner John Yates felt it had to investigate the possibility that Ms Turner was withholding documents critical to their case. Their main aim that morning was to search her home: it was hardly surprising that they did not first ring her up to make an appointment.

It's important to add that Ms Turner has released a statement declaring that she "utterly refutes any allegations of any wrongdoing of any nature whatsoever." I think she means "denies" rather than "refutes" but we get the point.

Other senior Labour politicians have ill-advisedly followed Mr Blunkett's lead in questioning the Met's tactics. The Labour peer Lord Puttnam called on the police to "put up or shut up" - a statement which would make sense only if the Met had been talking rather than taking action. The former Foreign Office Minister Denis MacShane accused the Met of "arriving at the door of a young sincere woman in a bid to make her crack". Normally the word "crack" in this context means "to blurt out the truth." Do tell us, Denis: why would that be such a terrible thing to happen?

There is no doubt that DAC Yates has been conducting this enquiry with a fearlessness which has taken Westminster completely by surprise. One reason lies in what happened during the last case which bought this unassuming-looking police officer to the attention of the wider public. I refer to the investigation into the alleged theft by Paul Burrell, the butler to the late Princess of Wales, of a number of his ex-boss's possessions.

Burrell's trial collapsed when The Queen suddenly revealed that Burrell had told her that he had taken Diana's possessions "to protect them." Yates drew the conclusion that if he had been less intimidated by the aura of the Royal Family, he would have questioned them more thoroughly, and thus avoided such a debacle. He was never likely to make a similar mistake again: he will not be intimidated by the Office of Prime Minister.

The fact that Mr Blair is Prime Minister is, in an important sense, irrelevant to the case. This is all about the Labour Party. Ruth Turner is purely a Labour party appointee and is paid by the party; this whole matter relates to loans - or possibly that should read "loans" - given to the Labour Party. In this context Mr Blair is not the Prime Minister; he is the chief executive of a business which might have perpetrated fraudulent transactions.

It was in fact not Yates' men - or so I am told - but the Serious Fraud Office, which discovered one of the more important pieces of evidence in this case. The SFO was already investigating Merlin Biosciences, the business founded by Sir Christopher Evans, one of those who had loaned, or "loaned", many millions of pounds to fund Labour's 2005 general election campaign. The SFO, allegedly, came across a note in Sir Christopher's handwriting about a meeting he had had with Lord Levy, Mr Blair's fundraiser extraordinary.

The note referred to the possibility of Evans receiving either "a K or a big P" - that is to say, either a Knighthood or a Peerage. Evans and Levy have been arrested by Yates's men; again, we must acknowledge that both have strenuously denied any illegality. For good measure, Lord Levy's friends have constantly emphasised that it is only Mr Blair who can ensure that any Labour donor is on the list of those proposed to the Queen for the honour of a knighthood or peerage: advisors advise, but Prime Ministers decide.

One of the more fabulous ironies in all of this is that it will be another former Labour donor with a peerage who will play a critical part in the decision whether or not prosecutions should follow from DAC Yates' investigations. The peer in question is Lord Goldsmith, the Attorney General.

Goldsmith last week furiously rebutted his colleague in the Upper House and the Cabinet, Lord Falconer, for assuring MPs that the Attorney General would not become involved in any decision whether or not to prosecute. Falconer, Lord Goldsmith told the Commons' Constitutional Affairs Select Committee, "was not in a position to give an 'assurance'... as to how I would act. No other minister, however distinguished or senior, has the ability to bind the attorney general in how he exercises his role."

Poor Charlie Falconer: he had only been trying to take some of the heat off his old flatmate, the Prime Minister.

Peter Goldsmith is especially sensitive to any suggestion that he is incapable of impartiality. As well he might be: this is the man who last month ordered the SFO to drop its investigations into allegations of illicit payments to Saudi princes by British Aerospace, on the grounds that "the wider public interest outweighed the need to maintain the rule of law".

This is also the man who having originally given as his judgement that "a Court might well decide that a further [UN] council resolution" would be necessary to authorise the 2003 invasion of Iraq, wrote a new opinion at Mr Blair's request which said that a further resolution was not legally necessary.

Through charm, patronage, and, if necessary, brute political force, Mr Blair has invariably managed to impose his own will on the British legal system. DAC Yates, however, will almost certainly know by heart a famous judgment given by Lord Denning almost 40 years ago: "I have no hesitation in holding that, like every constable in the land, the Metropolitan Police Commissioner should be, and is, independent of the executive... No Minister of the Crown can tell him that he must, or must not prosecute this man or that one. He is answerable to the law and the law alone."

d.lawson@independent.co.uk