Dominic Lawson: Blair's government is suffering deathly decay. Just look at all those pallid faces...

"Behold, a range of extinct volcanoes; not a flame flickers upon a single pallid crest." It was with those words that Benjamin Disraeli, pointing across to the front bench in the House of Commons, drew dramatic attention to the physical exhaustion of the members of William Gladstone's administration in 1872. A year later, that great reforming government fell.

David Cameron will be familiar with that remark by the founder of the modern Conservative Party. Indeed, I am a little surprised he has not yet tried an updated version of it during his televised question time exchanges with the Prime Minister. It is striking how Disraeli's metaphor so aptly describes the current front bench, whose leading members have been in uninterrupted office for the past nine years.

Mr Blair has a peculiarly pallid crest, try as he might to hide that fact with make-up. During his recent television appearances his face has had a haunted expression, and his skin seemed stretched to an unnatural sheen: I suspect there is a more natural colour on the face of the Prime Minister's waxwork effigy at Madame Tussaud's. When he entered office in 1997, he seemed to be the most vigorous 44-year-old in the country. Now he seems like the nation's oldest 53-year-old.

His deputy (at the time of writing) has just celebrated his 68th birthday. In the text of his interview with John Prescott in yesterday's Guardian, Michael White remarked that "he looks surprisingly well, relaxed even". It is unfortunate for the author of those words that his article was illustrated with a photograph of Mr Prescott in mid-interview. The word "exhausted" is insufficient to do justice to the shattered expression on the old pugilist's face. And as for the shadows under his eyes, they are not so much bags, as overpacked suitcases.

Gordon Brown's face is also ravaged by the marks of sleeplessness. But from his mouth downwards the Chancellor still exudes a characteristically intense energy - indeed his fingernails still betray it. Some may put this down to unsatisfied ambition. More likely, Mr Brown is blessed with an iron constitution. Perhaps it goes with the job. My father had the same position for six years, and was a government minister for 10; I was struck at the time by how unaffected he was by a decade of 18-hour working days. He told me more than once that the most important attribute for a politician was a strong constitution: "far more important than brains, or anything else you care to mention". At the age of 74, he has yet to spend a day in hospital. Perhaps Brown is made of the same stuff.

John Reid is another who still manages to display a sort of brutish energy, although his case is a rather unusual one. Whereas too many men (and women) in government become increasingly reliant on the dangerous consolations of alcohol, Reid has managed while in office to wean himself off both the bottle and the cigarette. Now he wakes up every morning knowing who and where he is - which is more than can be said for many people after they have been too long in government.

The good news for the families of exhausted Labour cabinet ministers is that this condition is easily reversed. Sometimes it takes only a day. John Major was described as a "grey man", but towards the end of his period in office that description seemed to become more than merely metaphorical. His face had become so drained of colour that viewers of his party political broadcasts must have been tempted to adjust their television sets. Yet on the day after the 1997 general election, he could be seen in a box at Lord's cricket ground, and looked positively in the pink. Indeed, with all the members of his administration whom I saw shortly before and after their fall from power, the transformation from pallor to colour was dramatic.

With very long-serving prime ministers it can, sadly, be different. Harold Wilson became aware during his fourth term of office that his mental powers were waning at an alarming speed, and he wisely resigned. He gave no reason in public, but as a man who had always prided himself on a phenomenal memory, the truth must have been painfully self-evident. A similar fate appears to have overtaken Margaret Thatcher, whose memory had been every bit as photographic as Wilson's. One of her close friends told me that her present condition was the inevitable consequence of the appallingly long hours she worked for such a sustained period, combined with the huge stresses of a unique style based so much on conflict, rather than consensus.

Another of her former circle told me that her error was not so much in the way she conducted herself in office, but in the fact that when she was cast out, she did not take a day's break, but stuck to her previous four hours of sleep a night schedule, immediately launching into a globetrotting series of speeches. Perhaps there is a warning there for a post-prime ministerial Tony Blair: not to say yes to every North American lecture tour invitation, however tempting the money might be.

The deathly decay of Mr Blair's administration seems to me to have more in common with Mr Major's than Mrs Thatcher's. John Major's problem was that, increasingly, he became seen by the public not as the leader of the nation, but as the leader of a political party - and a divided one at that. On the then central issue of Europe, it appeared that Mr Major's policies were designed not so much with the national good in mind, but simply to find a way of arbitrating between conflicting Conservative clans.

It is striking how this government's anxieties are now being described even by its own members as party rather than national matters. John Prescott's continuation in office (to the disgust of countless women voters) is openly justified on the grounds that his removal would necessitate an election for the deputy leadership of the Labour Party - as if the public actually cared about that. Des Browne, the Defence Secretary, last week publicly defended John Prescott's continuation in office, plus baubles, on the basis that "he has given a lifetime of service to the Labour Party". Does not Mr Browne understand that, on average, barely 300 electors in each constituency are members of the Labour Party?

Mr Cameron understands very well that the path to national political success does not lie in appealing to an atrophied party base. He is clearly aware that what he must do is to appear to be a potential leader of the country as a whole. This, in part, is why he is deferring the announcement, or even the creation, of policies: by their very nature they tend to divide the nation between those who agree with them and those who don't. Above all, I suspect he has recently re-read some other words of Benjamin Disraeli: "The Conservative Party, unless it is a national party, is nothing."

d.lawson@independent.co.uk