Dominic Lawson: This is more than a political knock-about – it's the inexcusable smearing of an opponent

The big smear started the moment David Davis announced his resignation to fight a by-election on the issue of Labour's erosion of civil liberties. It was said that Mr Davis had been "bewitched" by the director of Liberty, Shami Chakrabarti. The smear then grew, in the way these things do, to the allegation – unfounded, unjustifiable and, to any one who knows the happily married Ms Chakrabarti, unbelievable – that there was "something going on between them".

Over the last week it has seeped from the bars of the House of Commons into the newspaper columns. Ann Treneman, the Times' parliamentary sketchwriter, wrote a couple of days ago that "there is a rumour that David Davis resigned after being bewitched by Shami. She denied this, but then she would." I can see that this was designed to be amusing, but, if you were Ms Chakrabarti, then you could only be further distressed – and having spoken to her, I know just how upset she has been made by this innuendo.

Now, or so it seems, cabinet ministers are playing this poisonous game. In an interview with the New Labour magazine Progress the Culture Secretary, Andy Burnham, says of David Davis that: "I find something very curious in the man who was, and still is I believe, an exponent of capital punishment, having late-night, hand-wringing, heart-melting phone calls with Shami Chakrabarti."

Liberty's legal director, James Welch, observes with icy restraint: "We are very disappointed in this cabinet minister, who would not have said this if our director were a man."

Quite so: this sort of remark also carries the crude and condescending meaning that it is not through her articulate advocacy that Ms Chakrabarti, a Master of the Bench of the Middle Temple and a former Home Office lawyer, has mobilised political opposition to 42-day detention without charge – no, it's just because she's a babe.

Some see it as more sinister than sexist that Mr Burnham should be able to give such a precise description of David Davis's "late-night phone calls with Shami Chakrabarti": how exactly did the minister know what times of day such alleged phone calls took place? In fact, Ms Chakrabarti was quite open about the fact that she had spoken on the phone to Mr Davis after the vote on 42 days, when he told her of his plans to resign and fight a by-election; but the point is that she had tried to persuade him not to do so. Far from being "bewitched", Mr Davis ignored her and went ahead.

David Davis's own comment on Mr Burnham's remark is that: "Labour has now resorted to personal smears and lies rather than make its case for 42 days detention without charge and for the other illiberal measures it has taken." Quite so, again.

Nevertheless, in the interests of truth, or at least balance, let us put Andy Burnham's side of the story. First of all, his office insists that he is "aghast" at the very idea that he was imputing anything improper in the relationship between Mr Davis and Ms Chakrabarti. That was never his intention. Indeed, the minister was completely unaware even that others had made such a suggestion: Mr Burnham is in fact a holy innocent, or at least wholly innocent.

Furthermore, they say, we should study the interview as a whole, and put Mr Burnham's remark in context. So this is what the Culture Secretary went on to say to Progress, after his observations about Mr Davis's "late-night heart-melting phone calls": "Much is made of the intrusive state, the top-down state. I don't think we're on the wrong side of this with the public... When Labour councils have tested these issues locally they've always been pushed by the public to go further... On national security and terrorism, we mustn't be defensive about making these arguments, because the public supports us."

Very good; but if the public is so compelled by Labour's arguments, then why is the party completely unwilling to test them in the by-election that Mr Davis has called? This is a tinny echo of the claim made by Mr Burnham's boss last October, that the reason why he called off a general election at the last minute was that "we would win at any time". At least Gordon Brown had on his side the point that a general election was merely being postponed; but the by-election in Haltemprice and Howden has already been called. It can only be fought now and at no other time.

Labour, however, has ducked the very challenge Mr Burnham claims to welcome and on which he insists that it has the public's support. This has had the undoubted tactical benefit of making Mr Davis look even more like Don Quixote, tilting at windmills, rather than the real enemy. One of Mr Davis's miscalculations was failing to anticipate that New Labour would not stand and fight. He was under the misapprehension that they really cared deeply about these issues. Strangely – for he is very far from being a political innocent himself – David Davis underestimated their cynicism.

Mr Burnham's office put out a "clarifying statement" yesterday declaring that his remark about Mr Davis and Ms Chakrabarti was meant as "a light-hearted comment about the former shadow Home Secretary's political journey, by-election political knockabout and nothing else."

We have, it is true, become used to New Labour's conception of "by-election political knockabout". In the recent Crewe and Nantwich by-election, this involved pursuing the Conservative candidate, Edward Timpson, all across the constituency, with Labour party workers dressed up in Eton top hat and tails. They justified this on the grounds that Mr Timpson had gone to a minor public school and that his family had made quite a lot of money. It was a dismal failure, not least because the Timpsons are shoe-repairers rather than landed aristocrats, while the Labour candidate in Crewe turned out to be the one with a family entry in Burke's Peerage.

Still, if you actually take part in a by-election campaign, then you have the right, I suppose, to engage in such tactics. And if they don't come off, then you pay the price at the ballot box. Yet now New Labour have invented an entirely new doctrine: you don't deign to put your own candidate to the scrutiny of the public, but you still justify smears – sorry, "light-hearted comments" – against someone who is running, as being all part of the by-election process.

"No personal offence was intended to Shami Chakrabarti," concludes New Labour's "clarifying statement". Note the passive tense – the weasel way of appearing to apologise without actually doing so. The truth is that it is New Labour who are offended by Ms Chakrabarti: deep down, they simply can't accept the idea that the head of Liberty might actually be independent, that she doesn't know her place – which was meant to be in New Labour's big tent, and certainly not making common cause with the Conservatives. So they smear her.

d.lawson@independent.co.uk