Tony Blair's spin doctors are rightly famed. Yet every now and again they fail him. And so it must have seemed to the Prime Minister yesterday. Before the "centenary" conference, Mr Blair was busy trying to quash the latest comparisons between himself and Margaret Thatcher - and, more crucially, trying to prevent another outbreak of damaging warfare between the rival camps of 10 and 11 Downing Street.

"I want three terms as PM," rang one headline, as others invoked the language of an earlier prophecy to tell us Mr Blair planned to "go on and on and on and on".

Abandoning previous reticence, Mr Blair's official spokesman was reported to have confirmed that "Yes" the Prime Minister would remain throughout the whole of a second term, up to and including the subsequent general election. Mr Blair's determination to win an second term for Labour had never been in doubt.

Suddenly the talk was of a third term, a decade or more in office, and the prospect of Mr Blair equalling (if not surpassing) Mrs Thatcher's record.

The immediate thought was how that promise to "go on and on" had come to terrify the country (or at any rate the Tory party) and to haunt Mrs Thatcher - though admittedly only after her long reign should have been brought to a natural and mutually agreed end. The danger seemed more obvious still when the tale of vaunting personal ambition was read in conjunction with an Observer poll showing nearly half the electorate thinking Mr Blair already "too arrogant" after just two-and-a-half years in the job.

Mr Blair's immediate concern was to scotch suggestions that he had consciously decided to kill-off the Chancellor, Gordon Brown's continuing ambitions to succeed him. Relations have improved since the public confirmation of Mr Brown's sense of betrayal over the events following John Smith's death leading to the Blair succession.

But the latent tensions can be easily provoked, as in the past week with claims that Mr Blair was forced to apologise to his Chancellor for that infamous "Downing Street" portrayal of him as "psychologically flawed".

Mr Blair told BBC TV's Breakfast on Frost programme he had never pledged to seek three terms: "I have never said I want to be like Mrs Thatcher and go on and on and on." While not actually precluding the possibility, he said fairly that there was never really a sensible way to answer such questions.

As to reports that he had told Mr Brown he would never be prime minister, Mr Blair was dismissive: "It's complete rubbish. It's not for me to choose my successor. I know people are always trying to make mischief between us, but they never will."

They certainly will try. However, there should be no serious doubt about Mr Blair's determination to thwart them. The Blair-Brown axis is still the foundation stone of the entire New Labour project, the key to securing that second term, and to whatever happens thereafter.

Both will assuredly be singing from the same hymn sheet this week with explicit warnings to conference that they will not risk their reputation for economic competence by relaxing their grip on public spending as the economy improves.

Mr Blair gave a flavour of this at the weekend, insisting his very reputation for economic caution was the key to enabling his radical instinct - while holding the prospect that "at the end of a 10-year period, we will have seen a very significant increase in power, wealth and opportunity in the hands of the many, not the few . . ."

THE Chancellor followed this yesterday with a warning that "irresponsibility on pay will lead to higher interest rates and fewer jobs." Setting his face against any left-wing pressure for a populist spending spree, Mr Brown said he had no interest in "a shining moment" but sought a "permanent transformation in the British economy."

This stance could deepen the disillusion registered by the ICM poll. A third of Labour voters apparently believe the government has already broken promises on health, poverty, transport and combating sleaze. The near-loss of Hamilton South to the SNP, and the abysmal 25 per cent turnout at Wigan on Thursday, have renewed concerns about alienation in Labour's traditional heartlands.

There will inevitably be challenges to the platform this week over issues such as the privatisation of the post office, public sector pay and conditions, and the failure to balance rhetoric with practical plans to reduce significantly social exclusion.

But Mr Brown will balance his resistance to short-term measures by holding aloft "the great prize of full employment in the 21st century." On Tuesday Mr Blair will hammer home the relentless message that the choice for the comrades is not "the Labour government of their dreams" but between his and a Conservative administration.

As to that prospect? Yesterday's poll does reveal the flabbiness of Labour's underbelly. In six key areas where he promised change, voters say Mr Blair is failing to deliver. As attention begins to focus on Mr Brown's "war chest", the public demand is for radically improved public services, even if that means putting tax cuts on hold. Coupled with that perception of "arrogance", Peter Kellner ventured in the Observer that "if the economy were to falter, and the Conservatives were able to provide a more credible opposition, then Blair's government could be in real trouble."

The tensions between Mr Blair's two constituencies - traditional Labour voters, and the Tories who put him in last time - are obvious. However, the betting is that the Chancellor will keep faith with the latter, the government calculating that the former have nowhere else to go. The economy could always go wrong. However, on current forecasts Mr Hague must fully expect to be trumped by a pre-election tax cut.

As for the other big "if"? No one can take the electorate for granted, and the Conservatives might suddenly get lucky. But for as long as so many of them are preoccupied with the leadership prospects of William Hague, Ann Widdecombe and Michael Portillo, it will be difficult to believe them in serious contention.