Mr Blair, leadership and the great deception at the heart of our politics

The received wisdom is that a party leader who sets a limit on his or her longevity becomes an instant lame duck

Of all the many lawyerly evasions of the past few months, Lord Falconer's assurance at the weekend that his old friend Tony Blair would fight the next election "on the basis that he will stand for a whole term" is one of the more forgiveable. It's fair to ask whether it was wise to risk the charge of hubris by making such a prediction in a period of maximum fragility. But if Lord Falconer wanted - or was told - to get the message out that Blair was indeed intending to lead his party into the next election, it was no doubt sensible to pre-empt the second question, which would be: "Does he intend to stand down after the next election?" And to do that, it's hard to see, in these challenging circumstances, what better formulation he could have contrived.

But in doing so, he pointed to a peculiar difficulty of the British system as it affects prime ministers confronting, as they all do sooner or later, the growing sense of their own political mortality. The received wisdom of the political classes is that a party leader who sets a limit on his or her longevity by promising to stand down in their next term becomes an instant lame duck. And to do it before an election that the leader does intend to fight is also to invite the "pig in a poke" argument - that a fraud is being perpetrated on the electorate because it is being asked to vote for one leader when in reality it will end up with another.

To avoid this undesirable outcome, modern Prime Ministers now choose to maintain for public consumption what history shows to be a complete fiction, namely that they could never surrender or lose office other than by being defeated in a general election. The exquisite ambiguity of Lord Falconer's phrase "on the basis" nods obliquely to the absurdity of this fiction. But it doesn't extract Tony Blair from the dilemma of what he himself says about his future at the time of the election. Assuming he gets there, of course.

I know a little about this taboo on prime ministers predicting their own departure, having been a first-hand witness to Margaret Thatcher's one attempt to break it. In early November 1989 I asked her in an interview for the Sunday Correspondent whether she would go on to fight not only a fourth election but a fifth.

One of her parliamentary acolytes suggested subsequently that this had been a cunning attempt to stitch her up. If only. In fact the question arose because one of her closest cabinet allies had told me a few months earlier that so energised was she after a decade in office that she was already thinking about a fifth term. However, this was now the week after the resignation of her then Chancellor Nigel Lawson, one of the worst moments of her premiership to date. She paused and uncharacteristically lowered her gaze towards the floor before saying: "No, because I think that people would think it was time for someone else to carry the torch."

That was a result, though, as it would turn out, a relatively short-lived one. In his memoirs, Lord Baker, who was then the Tory chairman, describes how when he asked her why she had done it, she replied: "I had to say it, Kenneth. When I said before the last election that I would 'go on and on', I was accused of being arrogant... There must come a time when I should stand down, and I have cleared the air. After the next election, other people will emerge as possible leaders, including your own good self, Kenneth."

Baker goes on to describe the deep dismay among "the loyalist right of the parliamentary party" that she had "not only fired the starting gun in the leadership succession stakes but had also imperilled the party's election prospects", since if she was to step down in the next term, "who would the voters who had supported her be getting as a successor?" .

As Baker recalls, Neil Kinnock, the then Labour leader, seized the moment, arguing both that she would be a lame duck and that the electorate would not know for whom they would be voting. Baker then persuaded her to give another interview, to Robin Oakley of The Times, in which she (this time more characteristically) declared: "I have had so many protests about my answer that by popular acclaim I am quite prepared to carry on." As Baker says, this made matters even worse since her critics, silenced by her first remark, now felt provoked by the second. So in yet a third interview, this time with David Dimbleby on the BBC's Panorama, she used a formula, devised by Baker's own adviser Tony Kerpel, that had, in Baker's judgement, the "desired" effect: "I would like to go on as Prime Minister," she declared, "for as long as the electorate and the party want me to."

In the end of course - a cautionary tale, this - the fuss was all academic. She did not even make it to the next election, held in 1992. But assuming Blair does, this formula may yet be the best that Blair can manage. There are disadvantages for him that didn't obtain in the Thatcher case. By tilting against an entirely voluntary departure, it cuts across what used to be the appealing assumption that here is a man who isn't obsessed with politics and can easily envisage a life outside it. And whereas "the party" - or rather the party outside parliament - mostly hungered for Thatcher to go "on and on", that can't as reliably be said for Blair, who would with such a formula be publicly conferring on it a veto on his own hold on power.

Nor, in Thatcher's case, was there an obvious successor, a Gordon Brown brooding in the wings. Blair can hardly say what may be true - that he will be ready to go after the euro-referendum he still yearns for. Maybe he can come up with something better. Maybe he is still genuinely contemplating a full third term. But either way, two points stand out. One is that it will be a sharp question in a way that it wasn't the last time around. And secondly that there are no easy passes, when it comes to answering it, between the rock of arrogance and the hard place of weakness.

Not now, and not in Britain, anyway. In Spain, Jose Maria Aznar may have set an inspiring example to future European politicians by unusually insisting, way back before his first election in 1996, and then repeating it five years later, that he wouldn't allow himself to hang on, as Felipe Gonzalez had, beyond two terms. And - as far as anyone can so far tell - by sticking to it. Aznar so dominates his party, of course, that he too has ensured no obvious successor looms behind him.

But maybe proscribing unlimited office for yourself is the way to do just that - pointing to a future in which European, including British, leaders set boundaries to their own longevity by custom as the US system does by law. Either way, however, there needs to be some way out of the deception that remains central to this open-ended system, and requires that leaders can't (as well as often won't) admit their own political mortality. If there was, then perhaps some of the other institutional deceptions of British political life would disappear with it.

d.macintyre@independent.co.uk