By Nick Assinder BBC News Online political correspondent

Gordon Brown has relished his reputation as one of the most successful post-war Chancellors.

And he clearly doesn't like the fact that it is now seriously under threat.

He is doing his best to blame his massive hike in borrowing on events beyond his control, but it simply is not washing.

And, for the first time since he entered No 11 Downing Street, he is facing the sort of criticism Tony Blair puts up with on a regular basis.

He is being accused of deliberately offering overly-optimistic forecasts of the way the British economy will develop over the next few years - just as he got it wrong last time.

Nightmare scenario

This time it is far more serious for him. If his figures are wrong again then the impact will come just as he should be preparing voters for the next general election.

The nightmare scenario for him and the government is that, in two years' time, not only will his forecasts have proved wrong and he will be facing the choice of cutting spending or raising taxes - but that there will still be few signs of things actually getting better in the public services.

And the excuse that he just didn't see the problems looming will not hold any water.

Indeed, he had trouble convincing the city and business that he could not have seen the current juggernaut heading straight for him.

Brown: keeping a grip

He attempted, in his pre-Budget statement, to convince everyone it was the slump in the world economy, stupid.

But many find it incredible that he could not have predicted the global slowdown. Others were doing so.

Of course, if he had, his growth forecasts at the last budget would surely have been very different . Possibly even closer to some of the independent forecasts being bandied about at the time.

And he may have found it more difficult to justify his massive public spending programme.

Deadly dull

Luckily, everyone knew the Chancellor was going to have to downgrade his forecasts, because he has been whispering it to anyone within earshot for weeks.

Similarly, everyone also knew that he was not going to fill the hole by cutting spending or increasing taxes - yet.

Indeed, the Chancellor and his team have been spending much of the past few weeks preparing their excuses for this pre-Budget statement.

And he started his otherwise deadly dull statement trotting them all out.

The global economic slowdown, the aftermath of September 11, events surrounding Iraq, the troubles in the IT sector have all played their part.

Howard enjoyed himself

But, thanks to his brilliant handling of the economy - prudence, stability and so on - Britain is in better condition that any other country worth mentioning, he more or less said.

That is, as it happens, accurate to a degree - so long as there's nothing else around the corner that he hasn't yet spotted.

Wide of mark

It is also pretty reassuring when the Chancellor says he can handle all these setbacks within the economic cycle.

And he was certainly at his reassuring best. Don't worry, I know what I'm doing and it will be alright, he told the country.

Blair: a small smile?

And that may well prove to be the case. The trouble is, many will now be asking the question: "why believe a word of it."

If his previous predictions were so wide of the mark what is to say he is not missing something now?

His shadow, Michael Howard, gave him no quarter.

These were the downgraded forecasts of a downgraded Chancellor.

This was a moment of humiliation for the Chancellor.

Everyone knew what was happening in the world except the Chancellor, he declared.

Wrong again

Mr Brown has, in characteristic form, brushed all this aside insisting that, thanks to him, Britain is strong enough to weather the storms without threatening his spending plans.

But there can be no doubt this was the most difficult statement he has yet had to make at the despatch box - and that this really is a test of his competence as Chancellor.

If his figures are right this time around, he will emerge pretty much intact and with his spending programme untrimmed.

If he is wrong, again, then his hard won reputation will be seriously, possibly fatally, damaged.

It is not a reassuring thought to suspect that he has his fingers crossed.