Jack Straw is trying to sound tough, and cunning. The Foreign Secretary has let is be known that if British interests were at stake, he would go into battle against the European Constitution, as drafted by Valéry Giscard d'Estaing.

Mr Straw has gone so far as to say that it is not essential to adopt the constitution. If the final draft were to contain items which the UK found unacceptable, the government would be prepared to cast a veto.

That is strong stuff. It is also strongly unconvincing. Jack Straw is merely indulging in a tactical ploy for a domestic audience. It may deceive some elements of the British electorate. It will not deceive anyone in Brussels, partly because the ploy's provenance is self-evident. Tony Blair has long since become his own foreign secretary. But as he has no wish to humiliate Mr Straw, the Prime Minister graciously bids him to take part in the decision-making process, even though he is never allowed to take the decisions.

Mr Straw has never chaffed at these restrictions. Perhaps he knows his own limits too well. He will barely express his preferences in breakfast cereals without clearing the matter with Number 10. So it was Number 10 which instructed him to express his doubts on Giscard.

This will not unduly alarm either the former French president or his many supporters in France and Germany. They know that Tony Blair himself is absolutely committed to a European Constitution; he has given them many assurances on that subject. Not only that: Giscard's principal draftsman, Sir John Kerr, was a former head of the Foreign Office, recommended by Mr Blair. From the outset, Tony Blair has been closely and approvingly involved, as have some of his closest advisers.

While John Kerr was doing the writing, Sir Nigel Sheinwald was the British Ambassador to the EU. Sir Nigel is a Euro-zealot. A few months ago, Mr Blair had to select a new principal adviser on foreign affairs. His choice fell on ... Nigel Sheinwald. There is no need to bring in Sherlock Holmes; the dimmest plod in the Metropolitan Police could find Tony Blair's dabs all over the European Constitution, and he is determined to pass it into British law.

Before that, however, he has one problem: British public opinion. A few months ago, there was another leak from the Foreign Office, and on this occasion it was not a tactical ploy. It became apparent that the government was terrified of the tabloid press. The fear was that the Mail, the Sun and other newspapers would lead the demand for a referendum, before any European Constitution passed into law. Mr Blair does not wish to hold such a referendum because he thinks that he would lose it. This Monday, he was hoping to dissuade Jacques Chirac from holding a similar vote in France. That would have been bound to arouse anger in the UK: the frogs allowed to express their views, while we were dragooned by the Labour government's whips.

Conniving with a French president to suppress democracy is a shameful role for a British prime minister, but on this occasion Mr Blair found a receptive audience. The French president is uneasily aware that his popularity is seeping away and that many French voters would relish an opportunity to deflate him.

So Mr Blair may have neutralised the French. Mr Straw was the week's second gambit. He was instructed to try to neutralise British opinion. He was supposed to sound implacable, while insisting on concessions from the foreigners. He was doing this, of course, in the certain knowledge that he would be granted a few minor drafted amendments, which would change nothing of substance. But he could then trumpet those as a great victory for Britain, in order to head off calls for a referendum.

It was a good try. It was also a transparent one, and as such, unlikely to deflect the British public from an increasingly settled conviction. More and more people are coming to believe that Europe is a continuing plot against British interests, and that pro-European ministers -- such as Mr Straw -- cannot be trusted to tell the truth.

There was a further problem. Even if Jack Straw were seriously interested in altering the constitution, he would find no allies on the continent. The Giscard exercise is a federalising one; a further phase in France's ambition to run Europe as a French jockey on a German horse. If Tony Blair is prepared to acquiesce in that, and is merely seeking some rhetorical camouflage to disguise his intentions and mislead his own voters, the Franco-Germans will oblige him. If he really wanted changes of substance, he would be ignored.

As he is not seeking substance, he will be accommodated in verbal persiflage. But this is not a defence of British interests. This is a betrayal of British interests.