Prince Charles is feeling the force of a newly emboldened Cabinet

It was one of the finest examples of praeteritio in recent political history. Thanks to the great advances made in the British education system under the Labour Government, otherwise known as Google, we are all familiar with the devices of Greek rhetoric. Praeteritio, done well, is one of the best. It means emphasising something by claiming to pass over it. At its crudest, it is a way of pretending to be positive while being negative, of attacking your opponent by listing all the things you are not going to say about him.

It was one of the finest examples of praeteritio in recent political history. Thanks to the great advances made in the British education system under the Labour Government, otherwise known as Google, we are all familiar with the devices of Greek rhetoric. Praeteritio, done well, is one of the best. It means emphasising something by claiming to pass over it. At its crudest, it is a way of pretending to be positive while being negative, of attacking your opponent by listing all the things you are not going to say about him.

Thus Charles Clarke, the Secretary of State for Education, on the radio on Thursday: "I'm not going to comment on a private memorandum from the Prince but, on the issue, I'm against that approach to things."

The Prince of Wales, it emerges today, now accuses himself of misrepresenting his true views in the memo in which he railed against a junior employee's desire for promotion. He did not really mean to blame "the learning culture in schools" for telling people they can all be "top pop stars, High Court judges, brilliant TV presenters or infinitely more competent heads of state without ever putting in the necessary effort or having natural abilities".

The Greeks probably had a word for that, too, loosely translated as "putting one's foot in it by using one's own disastrous life story to lecture others about knowing their place". Prince Charles no doubt sincerely believes that he has put in the necessary effort, and possibly even that he has the natural abilities, required to be heir to the throne. But the other Charles thought it was intolerable for a man who, with all the benefits of an elite education, managed to obtain a B and a C at A-level, to accuse a secretary with a university degree of thinking she was qualified to do things "far beyond" her "technical capabilities".

So he said so. "We can't all be born to be king, but we can all have a position where we can really aspire for ourselves and for our families to do the very best we possibly can."

As he warmed to his theme, John Humphrys, the presenter of the Today programme, quoted more of the Prince's half-baked waffle, attacking a "social utopianism which believes that humanity can be genetically and socially re-engineered to contradict the lessons of history".

Clarke could contain himself no more. He carefully took off the top of his head and erupted. "As I say, I don't want to get in a tangle with the Prince of Wales. I decided before coming on to your programme this morning that I would try to discipline myself about his remarks." As a large part of the nation cheered their radios on, he cast aside the convention that ministers do not criticise the Royal Family. "To be quite frank, I think he is very old-fashioned and out of time, and doesn't actually understand what is going on in the British education system at the moment. And I think that he should think carefully before intervening in that debate. That's what I really think."

Marvellous stuff, which forced the Prince to rewrite tomorrow's speech to "clarify" his views. But there is more to this than knockabout entertainment. Politics is changing. The Prime Minister's announcement that he will not fight the election after next has lifted the constraints on ministers - not much, but appreciably.

Clarke is a naturally combative politician, and might have gone for the Prince anyway. But it was interesting that John Reid, another combative politician, joined in the next day, publicly agreeing with his Cabinet ally in a pre-recorded interview shown on Channel 4 last night. It was not until Peter Hain, the Cabinet minister best known for his republican sympathies, took to the Today programme on Friday that the old restraints started to be reimposed. He refused to be drawn into the fun.

Downing Street had gone into firefighting mode to try to cool the story down, but without the urgency of yesteryear. I am told that Tony Blair was not really bothered by the fuss. One of his advisers admitted that Clarke's language was "florid", but wondered whether it was going to continue to be the case that "people in public life will not engage with the Prince". Compare this with the touchiness of Blair's inner circle about the monarchy in opposition and in the first term of government, when Ron Davies and Mo Mowlam were given the third degree for deviating from the New Labour, New Royalist script.

There is a cool draught of the fresh air of liberation drifting into the Cabinet room. The atmosphere in Cabinet is beginning to resemble that in Year Six of primary schools around the country. The pupils know they are leaving next summer, and that they will never have to see their teachers again. It is becoming noticeably more difficult to maintain discipline.

That is not to say that Clarke was, in the florid language of headline writers, launching a leadership bid. His comments about the Prince will have gone down well with all three sections of the electoral college that will elect the next Labour leader - MPs, party members and the four million trade unionists who support the Labour Party. More importantly, they will do Clarke no harm at all with the hidden fourth section of the electoral college - public opinion as mediated by opinion polls - which will have a decisive influence on the way the first three sections vote. But that does not automatically mean that Clarke's attack on the Prince was premeditated. Indeed, the most plausible interpretation is to take the Secretary of State at his word and assume that he went on the Today programme intending to hold back, but then decided, live on air, that the Prince's views were so ridiculous that he let fly.

So it is too crude to describe the increased activism of leading members of the Cabinet - Clarke, Reid, Hain, Alan Milburn, Jack Straw (but not Gordon Brown) - as a leadership contest already under way. It is more that, as John Prescott put it, the plates are shifting. The political landscape is being subtly reordered as new assumptions take hold. The significance of Blair's "no fourth term" announcement has, if anything, been under-reported. It has liberated the contenders for the succession to lurch to the left, when they feel strongly about something and when they calculate that there is a populist advantage to be gained by it.

Blair's announcement has achieved its purpose: to suppress speculation about tension with the Chancellor before the general election. But there is a risk that the Prime Minister will be quickly weakened after the election. And there is a price to pay now, in the pervasive sense that Blair is living on borrowed time. He borrowed the time from the Chancellor - in that sense, he's living on Gordon's time. But it is time that will expire, and either revert to what the Chancellor's supporters regard as its rightful owner, or to a rival who happens to be in the right place when the music stops. We look forward to further displays of brilliant rhetoric - "n., the study of speaking as a means of persuasion".