How Tony would manage without Gordon

Tony Blair is fond of telling his ministers to "think the unthinkable". Perhaps he now needs to do so himself. The old story about his fraught relations with Gordon Brown has resurfaced in a new, more intense form over the past few days. One ex-minister, the everpugilistic Frank Field, has called on the Prime Minister to sack his Chancellor.

Mr Blair won't do that - at least not yet, and not unless provoked beyond endurance - but there is a growing sense that an era in Labour politics may be moving towards an end. Even if Mr Brown is not pushed, he may jump, possibly because he finally decides he is unlikely ever to become Prime Minister. He has already toyed once with the possibility of running the International Monetary Fund. He could be an inspirational leader of the World Bank. He would still nurse his resentment at failing to achieve his lifelong ambition, but he would not pose any threat to Mr Blair.

He would, however, leave a huge gap. The Prime Minister means it when he calls Mr Brown "one of the finest finance ministers in the western world". No successor could hope to wield anything like the same power. He (or, just possibly, a ground-breaking she) would be subordinate to Mr Blair in a way that Mr Brown has never been.

If a mobile phone starts to ring in the audience during one of the Prime Minister's speeches, one of his stock jokes is to say: "Tell Gordon I'm not making any new spending pledges." He is unlikely to raise a laugh saying "tell Charles", or "tell Patricia".

The first big effect, then, would be for Mr Blair to seize the same control over economic policy that he already enjoys over every other part of policy-making. Whenever important new initiatives have been needed during the past four years, Mr Blair has taken charge. Think of the Northern Ireland peace process, or the fight against foot-and-mouth, or Kosovo, or plans to reform the health service, or, now, the struggle to defeat global terrorism.

Just as he occasionally takes over nowadays as his own Secretary of State for Northern Ireland, Agriculture, Defence, Health or Foreign Affairs, so he would become First Lord of the Treasury in fact as well as honorary title.

This is unlikely to daunt him. Had Mr Brown been run over in the early days of this Government by a number 11 bus charging around Parliament Square, the Prime Minister would have been as upset as the currency markets. He, and they, relied heavily on Mr Brown's skill, judgment and intellect.

Today, Mr Blair has acquired enough authority, confidence and general experience to manage without the Chancellor.

Whether an all-powerful Prime Minister would be good for Britain is another matter. Already, as the past few days have shown, the air is thick with complaints that Mr Blair is "too presidential". If he finally captures direct control of the Treasury, the complaints are bound to flow with yet greater force. In practice, his staff at Number 10 Downing Street would become even more powerful than they are today. Already, the two most potent words in Whitehall are "Tony wants". The only known defence is the fourword question: "What does Gordon think?" With Gordon gone, "Tony wants" will be a virus without an antidote.

In terms of government strategy, three changes are probable if the Chancellor departs. The first - in the unlikely event that Mr Brown goes within the next few months - is that Mr Blair would seek to make peace with Ken Livingstone over the future of London's Underground. The Prime Minister has never been as stubborn as Mr Brown about sticking to the public-private plans that have proved so unpopular; nor does he regard London's Mayor with the same personal animosity as does the Chancellor.

Second, Mr Blair would require his new Chancellor to make cash for public services a higher priority than more generous welfare payments. For all the talk about New Labour and wooing Britain's middle classes, Mr Brown has done far more than any previous Labour Chancellor to help the least well-off, partly by removing many of the tax breaks (such as mortgage tax relief) that used to be cherished by Middle England.

He has not finished, and is currently arguing with the Prime Minister about how much extra money to apply to the new Children's Tax Credit and, in due course, the new Integrated Child Credit. Despite their ungainly names, these are truly radical measures in the fight to end child poverty. If Mr Brown departs, their greatest champion will be gone.

Third, and perhaps most important, if the Chancellor goes before the end of next year, then a referendum on the euro in this Parliament will become a near-certainty. As long as Mr Brown stays at the Treasury, he has the ability to block Britain's entry into the single currency. No Prime Minister could expect to win a referendum on this issue if his Chancellor was known to be hostile; in practice, therefore, Mr Blair could not take the risk of defying Mr Brown as long as the two men remain Downing Street neighbours. But a new, more enthusiastic occupant of Number 11 - that would transform the politics of the euro completely.

Of course, none of this may come to pass. Mr Brown may remain Chancellor until Mr Blair leaves office, even if that day is well after the next General Election. But since 11 September, something has changed in the ecology of this Government. Mr Blair's stock has risen, and Mr Brown's role as near-equal on the domestic stage has started to look more fragile. The prospect of Mr Blair carrying on without him is now real, even if no minister dare say so in public.