Alan Watkins: We know Mr Blair has a date with the setting sun. But doesn't Mr Brown, too?

The Chancellor is beginning to look like an unlucky PM

Our great leader has inaugurated a reign of terror throughout east London, contriving to have one or two suspicious characters shot, just to be on the safe side. These excitements, having palled, there is always the World Cup to look forward to.

It is one of the myths of politics that a previous leader, Harold Wilson, rode to victory on the backs of the England football team that had won the competition of 40 years ago. In fact the election was contested in March, whereas the cup was won in July, though he insisted on putting in an unscheduled appearance on the team's balcony in Kensington.

Equally, there is no hard evidence to support Wilson's decision to hold the election in June, 1970. What was more persuasive (as his adviser, Mr Joe Haines, told us) was that Wilson had decided to go to the country before decimalisation in 1971.

Even so, he had urged his followers to "clean up'' on their return from work - a usage that had previously been unknown to me in Wales - and, after a spell of gentle canvassing, to support "the lads''. Alas, it was not to be, and England were eliminated within four days of Edward Heath's win at the election.

The present parliament has only had just over a year since the election. With or without Mr Gordon Brown in charge, the Government has three or even four years in office. The phrase " in office, but not in power" was last heard from Norman Lamont after he resigned as Chancellor of the Exchequer in 1993.

As it happened, he was dismissed rather than resigned, but modern ministers are allowed to hang on to the trappings of resignation, even to the extent of being permitted to make a resignation speech from the back benches. Mr Charles Clarke at any rate had the decency to sit down and keep quiet; or, if he did not, I missed it.

But to return to Lord Lamont: the phrase was originally used of Ramsay MacDonald's minority government in 1924. Ministers said they were in office but not in power. The last Conservative government, of which Lord Lamont was briefly a member, went from a majority of 21 to a minority of three in five years.

When Lord Lamont was in the process of leaving the Commons stage, the Conservatives possessed a healthy even though diminished majority. In the 1970s, by contrast, there was mostly a hung parliament. In The Independent history is being rewritten before our very eyes. In October 1974, the Labour administration began its life with a majority of three and ended it in a minority of 17.

There are more or less two kinds of reason why governments run out of puff. One is that majorities melt away; the other is that ministers lose their enthusiasm; sometimes it is a mixture of both. Harold Macmillan had a large majority but became dispirited, left office through illness at 69 (though he had no real need to do so) and went on to reach the great age of 92.

Mr Tony Blair seems to be very strong, even if he may have had the odd alarm with his health. But, in any case, that is not the point. The years stretch ahead with thudding inevitability.

Mr Jack Straw, the latest candidate for deputy leader, tells us that the Prime Minister will stagger off the podium in 2007. Well, we have heard that one before. By the way, there seems to be a wanton confusion between the posts of Deputy Prime Minister and deputy leader. The explanation seems to lie in what Samuel Johnson once described as "ignorance, madam, pure ignorance''.

There have been only two Labour Deputy PMs, Herbert Morrison and John Prescott, with C R Attlee as Winston Churchill's deputy in the Coalition government. There has been a whole string of arbitrarily appointed Tory deputy PMs. But since ancient times there has been an apostolic succession of deputy leaders, in the post-war period all elected, and of greater or lesser degrees of ineffectiveness.

Mr Straw has never lost his gift for stating the obvious. That is one of his great political strengths. Mr Straw has advanced the year by 12 months. That is the only substantial modification. He has also proposed that the deputy leader should go down the aisle afterwards with Mr Brown, with Mr Straw as the blushing bride; or better, perhaps, as the pretty bridesmaid.

How can one put this? But are they, possibly, too old for this kind of performance? Instead, Mr David Cameron has been handed the bridal bouquet. For my part, I cling to the truth that, once a PR man, always a PR man.

I see that Mr Cameron has taken to flying the St George's flag from his bicycle for the duration of the World Cup or, at any rate, for its preliminary stages. Mr Blair has been doing something similar on government buildings, though he lacks quite the personal touch.

The St George's Cross used to be flown on obscure English parish churches, but Wilson's (not to mention Sir Alf Ramsey's) brave lads used to be supported solidly by the Union Jack. The Union Flag was supplanted in the 1990s by the red cross on a white ground, so emphasising the qualities of English nationalism, the British National Party and general disobligingness. Mr Brown is paying tribute to England too. Even Dr John Reid will be persuaded to join the cheering throng before very long.

The truth is that Mr Brown is beginning to look like an unlucky Prime Minister. It is a matter almost wholly of longevity. James Callaghan had just over three years in Downing Street, while Anthony Eden had a year and nine months, and Alec Douglas-Home a year only. Eden went to the country within seven weeks of Churchill's retirement in 1955 but was in office only until January 1957.

There would be a temptation for Mr Brown to do likewise. Instead of playing fag-end of Mr Blair's audience he would have what his supporters wanted, a fresh mandate. In 1955, the Churchill Government would have run its course: the decision was taken by the apparatchiks at Central Office to go while the going was good. There was nothing wrong with the reasoning except that Eden went off his head later on, though the position was remedied by Macmillan.

It would be imprudent in the extreme if Mr Brown took any risks with his majority. After all, we - or, rather, the Labour benches - have become accustomed to governing with large majorities. Mr Blair or Mr Brown will still be comfortably off. And yet, I feel it somehow, not only that Mr Blair will shortly be off into the setting sun, but that Mr Brown will be off as well. It is just a feeling that I have.