The necessary condition for inclusion in the list is a fair spell in No 10. Thus Attlee had six years, Macmillan six, Wilson eight (broken into two periods) and Lady Thatcher 11. But length of tenure is not quite sufficient. After all, Mr John Major was there for longer than Attlee or Macmillan. I doubt whether people will ever talk about the age of Major.
At the same time, it is not necessary to have made some unquestioned contribution to history. Of the four prime ministers, historians now agree that only Attlee and Lady Thatcher unarguably deserve a permanent position in the first division, though they dispute the order of their placings in the table.
But this estimate may be no more than this year's fashion. There is a case for saying that the country we live in today is more the work of Macmillan than of anyone else. There are even some eccentric characters who are prepared to try to make out a case for Wilson as a great prime minister. There is no need to go quite so far as this. It is enough that he, like Macmillan, lends his name to an epoch, an age. When we talk about the age of Wilson, we know more or less what we mean.
Will there be an age of Blair? Will the Millennium Dome come to symbolise it as the Skylon at the Festival of Britain of 1951 symbolised the age of Attlee (destroyed as it was by the malignity of Churchill's government)? Re-reading J M Thompson's history of the French Revolution, I came across a similar project during Robespierre's Terror: "A public competition was advertised for designs for roofed arenas, in which, during the winter, the triumphs of the republic could be celebrated by patriotic community- singing."
Well, that is certainly one purpose to which the Dome could be put. Mr Peter Mandelson and his advisers seem distinctly short of ideas. And Mr Mandelson, like Robespierre, has a thin-lipped, puritanical quality about him. In similar fashion, Mr Tony Blair is liable to invoke the Sovereign People to justify whatever it is that the Government wants to do at any given moment.
As I have written before, I do not approve of this bossy note that has come into our public life, even though it was anticipated by Mrs Virginia Bottomley and one or two others in the previous government. But if the members of this administration are going to be puritanical about the rest of us, they might make a start by exercising some self-denial with themselves.
This is not a complaint about their eating or drinking habits. In fact - by which of course I mean, as people usually do when they use the phrase, in my opinion - they would be rather better at their jobs if they let themselves go a bit more. With the honourable exception of Lord Irvine, there is not one member of the Government who can approach the standards of relaxation set by Anthony Crosland, Richard Crossman and Denis Healey in the Wilson administrations; to say nothing of Michael Stewart and Ray Gunter, both of whom were, unlike the first three politicians, in a state of permanent semi-inebriation.
No, the trouble is not drink: quite the opposite. It would, as I say, be better if they drank a little more. Rather the mischief lies in all the redecoration that is being done and all these foreign trips that are being made, usually with what travel writers and restaurant critics call a companion. It does not seem to me to matter in the least whether the person who is filling this position is wife, mistress, husband or lover, or whether the couple are living together. I am reminded of the then foreign editor of a national newspaper, Mr Frank Giles, and his wife Lady Kitty attending a diplomatic reception in Moscow. As they entered a major domo announced:
"Mr and Mrs Frank Giles."
"Actually," Mr Giles, who was quite pleased to be married to the daughter of an Earl, said to his host, "she's not Mrs Giles."
"Don't worry about that, Frank," the host replied. "We're very broadminded here. Just get a drink and enjoy yourselves."
Questions of Procedure for Ministers looks precise but is vague. What is called a "spouse" can be paid for by the taxpayer if it is "clearly in the public interest that he or she should accompany the minister". This can mean anything and usually does. But there is a more objective criterion: whether the production of a companion is expected at the dinners, receptions or what-have-you that are being laid on by the host country. This is a test which Mr Blair might employ for his ministers and, come to that, for himself as well.
All this is meat and drink literally to ministers, metaphorically to the newspapers. Though the sums involved are tiny compared to those which any government regularly wastes in other ways, the redecoration of offices, the provision of free accommodation and the subsidising of foreign trips by ministers' consorts all help to convince the voters that this government is really no different from any other. "They're all the same" is a well- worn phrase that has been heard more frequently since, I suppose, last November.
Mr Blair himself still possesses a wonder-working quality, a magic ingredient. But the effect is wearing off, rather as modern drugs (I mean the variety approved of by Mr Frank Dobson) become less efficacious because the organisms which they are meant to counteract develop a resistance to them with the passing of the years. With politicians the process takes less long.
We may still remember an age of Blair, even if it lasts only four or five years. Sir Henry Campbell-Bannerman and, later, H H Asquith lost their majority of 130 in four years, Attlee his majority of 146 in six and Wilson his majority of 96 in four. Moreover, Mr Blair's majority of 177 was obtained through the votes of only 32 per cent of the electorates of England, Scotland and Wales. I have always thought it gives a more exact picture to take the number of people qualified to vote rather than the number voting, and to eliminate Northern Ireland because there, happily or alas, the British party system does not operate - indeed, it is not allowed to operate.
If the age of Blair comes to a premature end it will be because of the activities of the voters rather than the ambitions of Mr Gordon Brown. There is a first time for everything. But not one single Labour prime minister has ever been deposed (for Ramsay MacDonald deposed himself by forming the National Government).
Attlee was implored to stay on after the 1955 election, which he did briefly. Lord Callaghan did likewise for a somewhat longer time after 1979. Wilson went voluntarily in 1976 in a resignation which, far from being mysterious, had been planned by him years in advance. There is no reason why Mr Blair should not go in the same way. He may even emulate Wilson and depart at some point during his second term because his wife, Ms Cherie Booth QC, wants to become a High Court judge.