Alan Watkins: Maybe Mr Cameron thinks he can get his way without the crustier Tories noticing

Throughout his time as leader, a whole 12 years and - who knows? - several more, Mr Tony Blair has followed one principle; or perhaps it is more a rule of thumb, a guide to practice, than anything of a more exalted nature. It is an adaptation of Marxism: Nothing to the Right.

Thus a succession of Tory leaders, five of them by now, have taken up the space traditionally allotted to Conservatives, so that they have been squeezed into a stationery cupboard. Only now, with the latest promising lad, has Mr Blair felt the pressure on office space. Mr David Cameron has tried to escape the crush. Alas, the Bromley by-election shows little sign of a Cameron revival.

But Mr Cameron is certainly showing every sign of embarrassing Mr Blair. When the Leader of the Opposition brought up the Trident missile system - or, rather, the successor to that system - Mr Blair preferred to discuss Mr Cameron's replacement for the Human Rights Act.

This was a diversionary piece of tactics, but Mr Blair was allowed to proceed part of his way before being any further impeded by Mr Speaker Martin. One point of view is that the Prime Minister should have been made to keep quiet; another is that Mr Cameron is perfectly well able to look after himself. In the event, Mr Speaker adopted a compromise which seemed to satisfy all parties.

The odd thing was that Mr Blair was left looking more uneasy about the Human Rights Act than Mr Cameron was. The whole story is quite complicated. I shall try to untangle it as best I can.

For most of the post-War period, political discussion of human rights was dominated by what Mr Michael Frayn called the herbivores. The subject was monopolised by the old Liberal Party, by the new SDP (though it contained several statist sympathisers) by readers of The Guardian and The Observer (for the Independent newspapers had not then been invented), and by semi-detached Tories, who could be found on the fringes of the Bow Group and the Inns of Court Conservative Association.

There was a certain overlap between enthusiasts for human rights and for electoral reform, though the two categories remained distinct. Similarly, the European movement was sympathetic to human rights. But the official Conservative Party, at that stage fully paid-up Europeans, had to tread warily. For the human rights movement came up slap-bang against the sovereignty of Parliament.

A good deal of time and trouble was spent in the early 1970s showing to everyone's satisfaction that Parliament, by which people meant the House of Commons, remained supreme. This culminated in the European Communities Act 1972. It was delusion, as it was clearly meant to be. The Act unambiguously provided that, in cases of conflict, European law took precedence over UK law. Both the main parties chose to overlook the possible conflict between Europe and the UK. The principal quarrel that surfaced concerned certain Spanish fishermen, who obeyed European regulations at the expense of the domestic variety.

In the 1980s, the conviction began to grow on the Left and in parts of the Labour Party that the Conservatives could no longer be allowed to get away with whatever they liked. This was in contradiction to the old Labour philosophy that the party in power should rule unimpeded, whether by the opposition, the House of Lords, or the judges. It was the result of over 10 years of Margaret Thatcher. The 1992 Labour manifesto promised: "It is time to modernise Britain's democracy. Central to Labour's purpose in government is our commitment to radical constitutional reform. Our charter of rights, backed up by a complementary and democratically enforced Bill of Rights, will establish in law the specific rights of every citizen.''

But since 1949, British subjects had possessed the right to take their complaints to the European Court of Human Rights at Strasbourg. This had nothing to do with various new European institutions established by what used to be called the Common Market - and denounced with roughly equal degrees of fervour by the Daily Mail and Mr Rupert Murdoch's newspapers. Likewise, these very same papers are perfectly capable of remarkable feats of amnesia when presented with the supremacy of European law.

In 1992, Mr Neil Kinnock was quite ready to give us a Bill of Rights, though he may not have thought very hard about the matter. What happened during the 1990s was a process of elision. The incorporation of the European Convention on Human Rights became a statute. It was framed in 1998 and became law in 2000.

Mr Blair does not seem to have taken an active part in these matters, leaving Mr Jack Straw, the then Home Secretary, and Lord Irvine - a great reforming Lord Chancellor - to sort out these things for themselves. What Lord Irvine was trying to do throughout was squaring the circle of parliamentary sovereignty.

In the past couple of weeks, I have read several simplified newspaper accounts of the constitutional struggles of the 17th century. In truth, they are much stranger - conducted by odder people - than we seem able to imagine. The full development of the theory of parliamentary sovereignty took the first third of the 19th century to develop. For the last 40 years, the theory has been in retreat. This has come about partly because of the power of Europe and partly because of the influence of the judiciary.

Lord Irvine, however, took care not to offend the susceptibilities of the Commons. The "derogations'' from human rights legislation come and go, rather as succeeding Home Secretaries take account of the mood of the moment. Legislation can be presented to Parliament stating that the measure in question does not accord with the Human Rights Act.

For some years now, for about five years I would estimate, there has been a head of steam building up in the popular prints and, sometimes, elsewhere. It is perfectly fair for the cheap press and its allies to point to the excesses of the courts and the lawyers. But Mr Blair tries to have it all ways.

It is the same old trick. He denounces the foolishness of humane and enlightened opinion. Once Mr Cameron calls for the abolition of the Act, he defends it as the helpless infant of his new constitution. It may be a bastard, Mr Blair says, but it happens to be his own bastard.

Mr Cameron may now have a new child instead, the product of a committee of workers, peasants and intellectuals. The new arrival really would give the crustier Tories something to think about, if they bothered their heads with these things.