Mr Byers' latest brush with the truth goes to the heart of Parliament's role

The convention that you don't mislead the Commons is the bulwark against the falsehoods to which politicians are prone

The Stephen Byers saga was born and bred in the beltway. It has a cast of characters of which the public knows little and cares less. Having no relevance to the minister's responsibilities for transport – a subject about which the public cares a good deal – its real-world impact is negligible to zero. The point was at the core of Mr Blair's answers in the Commons yesterday, and there's a lot in it.

It is also, let's admit, a seductive story for Westminster journalists. It combines the thrill of the hunt with the safety of numbers. Because it concerns whether a minister told the truth – albeit about an issue that the most electors would regard as absurdly trivial – it invests the hunters with just the right amount of self-righteousness. The only obstacle it faces is growing boredom elsewhere with its sheer longevity.

What's more, a credible case can be made that the chronic attacks that have dogged and weakened Byers since the beginning of last October have something of the vendetta about them. Opinions about Byers' abilities as a minister certainly differ. But he has his stout defenders, some of whom see him as the victim of a concerted campaign promoted by shareholders bitterly disgruntled by the winding-up of Railtrack at their expense.

One of this government's more peculiar achievements has been to acquire virtually all the blame for the failures of a system taken out of its control by a privatisation forced through by its predecessors. But for that bizarre act of political masochism Byers is not the only, or even perhaps the main, culprit. It was already being committed long before he arrived at Transport.

Unfortunately, there is a little more to this – to most outsiders – arcane dispute over the details of his statement to the Commons on 26 February about a resignation by Martin Sixsmith, his director of communications, that had not yet happened. On Tuesday, in a joint statement agreed with Mr Sixsmith, Byers' department, expressed "regret" that "while acting in good faith" the department had announced that he had already resigned. And in an echo of the famous dictum of Ron Ziegler, President Nixon's spokesman, that "all previous statements are inoperative", it went on to cancel Byers' suggestion in his Commons statement that "Mr Sixsmith was not a suitable person to remain in government". Instead it declared that were it not for "these unfortunate events" (a dispute over a fake e-mail falsely supposed to have been from his special adviser Jo Moore, for which "no blame was being apportioned") Mr Sixsmith "would continue to be a successful director of communications".

Fair enough. As the terms of a settlement of a dispute with an employee against which no misdemeanour was, in the end, alleged, there is nothing abnormal about this. It was accompanied by a rather handsome pay-off for Mr Sixsmith of around £180,000. The problem was that Mr Byers did not yesterday personally come to the Commons dispatch box to explain himself – as he did the last time that he had also given a misleading account of aspects of the "unfortunate events".

Now for many people, not least the high command of New Labour, this no doubt seems to be piling trivia on trivia. How Ruritanian can you get? Why should a busy minister bother himself with a personal appearance in the Commons when his department had made a statement on Tuesday and the Prime Minister had defended him in the Commons yesterday?

The answer is that it matters a great deal, as Michael Martin, the Commons Speaker failed, at least initially, to realise when he obligingly turned down the first request from the Opposition for an emergency debate. It matters for several reasons, which badly need restating precisely because they seem to be so unfashionable.

For a start, the convention that you don't mislead, let alone lie to, the Commons is the one bulwark the British constitution has against all the obfuscations, fudges, and sheer falsehoods to which nearly all modern politicians are prone if left to their own devices, and by extension against the national cynicism that they generate. One of the ironies in the Byers affair is that to the extent that he has been undone, he has been undone if not by spin himself, then certainly by his spinners.

But the more importance politicians attach to parliament, the less they are likely to depend on spin. This applies, of course, to the (relatively) bad habit of making announcements to the press before they are made in Parliament. It applies much more to the need to explain and to defend. For example, Downing Street indicated on Tuesday that Mr Byers said what he did on 26 February because he had been so advised by his Permanent Secretary, the widely respected Sir Richard Mottram. Therefore he didn't wittingly mislead the Commons. If it was as simple as that, there was no reason whatever for not saying so to the Commons yesterday.

It isn't exactly a revelation to say that respect for Parliament wasn't exactly a priority for New Labour when they came in. The House of Commons didn't fit easily into Cool Britannia. And God knows, its cosy and hallowed customs are infuriating enough. But it's what we've got. The New Labour types, the Prime Minister among them, used to talk early in their first term rather a lot about "representative democracy" being only one kind of many relevant democracies – with a pretty clear implication that focus groups, polling and so on were equally valid ways of measuring public opinion. If that was what they meant, it was a violation of the constitutional truth. We do live in a representative democracy. And it's entirely right that a cabinet minister's ability to survive should, in the final resort, be tested there.

To be fair, the Government's attitude had belatedly begun to change – thanks in large part to a much more robust embrace by Robin Cook, the Leader of the Commons, of Parliament's true purpose. Cook has taken some significant steps – to be debated next week – towards making the select committees more independent. He has promoted the sensible use of draft bills, which means a good deal more scrutiny. Mr Blair's decision to appear twice a year before senior backbenchers is a real advance. But it rather torpedoes all this if a Secretary of State who admits he misled the Commons repeatedly, even if (as he claims) unwittingly, couldn't be bothered to explain himself to MPs. After all, last time he had only misled the audience for a Sunday lunchtime programme.

Mr Blair made a lot yesterday of the Tuesday statement's assertion that the misleading was done "in good faith". Mr Sixsmith, the potentially aggrieved party in other words, had ratified this interpretation. Well, it's no disrespect to Mr Sixsmith to say that I would be pretty understanding if I had just walked away with £180,000. Either Mr Byers has a robust enough case to withstand a parliamentary grilling or he should resign. If, as he surely now must, he appears before the Commons today, it's a pity he waited so long.

d.macintyre@independent.co.uk