by Andrew Marr BBC's political editor

If there's one political skill that Tony Blair possesses beyond ordinary measure, it's selling.

And after days of hostile and questioning headlines in the press about the Budget tax rises, he has thrown himself into the job of selling Gordon Brown's sixth Budget.

Speaking to me in Downing Street he vociferously denied that he had misled people about the possibility of tax rises during last year's election campaign.

Labour had given specific pledges and had broken none of them, he said.

Mr Blair told me it was a decisive moment for the government

Repeatedly, they had explained back then that they could not write Budgets in advance.

He had not known the scale of the investment needed because Sir Derek Wanless's report had just been commissioned then.

There is some justification for this.

During the election campaign, the BBC repeatedly questioned Gordon Brown and Mr Blair about possible national insurance rises to fund their spending plans during the lifetime of this Parliament.

No clear answers

They dodged giving clear answers and we reported them then as leaving the door open for NI and other tax rises later.

But no-one then was expecting quite this level of increase quite so early.

To that extent, voters are right to be surprised. Will the gamble pay off?

Mr Blair readily agreed that people would judge the Budget on the basis of how visibly the National Health Service had improved by the time of the next election.

He was "100% sure" voters would see real changes and he pledged that no-one would be waiting more than six months for an operation by 2005, against the 18 months some people had been waiting when Labour came to office.

Though he denies that this marks the end for New Labour or the return of old-style "tax and spend" Mr Blair told me it was a decisive moment for the government and one he'd long hoped to arrive at.

The word used most frequently about the Budget is "gamble" and for good reasons

After the years of economic stability, debt repayment and investment in education, it was at last possible to put serious investment into the NHS.

All the other systems around the world were more expensive or less fair than using general taxation; people understood that the question was not whether more money was needed, but simply where it would come from.

This is a government of brave faces, leading a party cheered that once more it knows exactly what it is for.

The enthusiasm of Labour MPs and activists is real, and they believe the Budget will help bring out traditional Labour voters who had been disillusioned.

But the word used most frequently about the Budget is "gamble" and for good reasons.

Turning point

If the economy makes a downturn, Mr Brown's numbers won't make sense.

If unemployment starts to move up again, those NI increases will be blamed.

And if by the next election the NHS is not a clearly better service, it may be the end for Mr Blair, Mr Brown, New Labour and a 50-year-old consensus on how to deliver Britain's health service.

There is nobody in the government or the opposition parties who'd deny that this week has marked a turning point in British politics.

The only trouble is, all of them disagree about in which direction we're heading.