By Nick Assinder BBC News Online political correspondent

Well she said she would resign if the government failed to meet the education standards it set for itself and Estelle Morris has now gone.

She has also clearly had enough of the strains and pressures of the top job and the recent glare of media criticism

But she has resigned from government claiming she had simply decided she was not meeting her own standards.

She was not up to the job and education deserved more than second best, she said.

But she has also clearly had enough of the strains and pressures of the top job and the recent glare of media criticism.

Many in Westminster believe she deserved to go over the series of disasters she presided over in the past few months.

And there were demands for her to do the decent thing at the beginning of this week, when her previous pledge to quit - and a later denial to a Commons committee that she ever said such a thing - was revived.

But there had been no indication that she was either about to resign or get dumped.

Huge surprise

Indeed, the initial furore over her most recent troubles had pretty much faded away and there was no major clamour for her head.

Ms Morris has clearly decided that her list of setbacks was partly because of her inability to rise to the top job

So the decision has come as a huge surprise and is bound to raise questions over what else may be looming.

There is a report on her individual learning accounts system due on Friday which could be highly critical.

And there was still the huge cloud over her in the wake of the recent disasters and a growing view that the loyal Blairite had been promoted too quickly and was out of her depth - something she was quick to deny after her resignation.

Blatant refusal

So it is thought that her demise may simply be the result of the cumulative effect of her past troubles, brought to a head by the timely reminder that she had promised to resign if numeracy and literacy targets were not met.

She will attract a degree of support, sympathy and respect for the decision she has taken

She first drew criticism at the start of the new school term when botched security checks on teachers led to delays.

She caused fury by describing some comprehensives as schools she would not touch with a bargepole.

She was blamed for the A levels fiasco that saw students downgraded, and her attempt to interfere in the expulsion of two pupils who threatened to kill their teacher also turned into a farce.

And, just as she appeared to have got away with that little lot, she was reminded of her rash promise in 1997 to resign.

It was the sort of pledge the still-euphoric New Labour government was always likely to make at that stage. But it was the most disastrous hostage to fortune.

Ms Morris has clearly decided that her list of setbacks was partly because of her inability to rise to the top job.

But she must also have realised that she was rapidly becoming an embarrassment to the prime minister and may have been due a reshuffle in the future in any case.

Memories of Byers

She would also have been aware of the danger of leading the government into another Stephen Byers situation, where there the spotlight was never taken from him after he failed to sack Jo "bury the bad news" Moore.

Virtually no week went by without another story appearing somewhere to embarrass the then transport secretary.

But whatever the reason, the prime minister will not be delighted.

He has an unfortunate record of losing ministers - Geoffrey Robinson, Ron Davies, Peter Mandelson (twice), Stephen Byers and now Estelle Morris.

The only comfort he will be able to take is that a minister is being seen to have done the right thing - even when she had already pretty much toughed it out.

It is highly unusual, if not unique, to have a minister admitting she is not good enough and giving herself the sack.

As a result she will attract a degree of support, sympathy and respect for the decision she has taken.

Mr Blair, however, is now facing the task of finding a new education secretary without, presumably, being forced into a major reshuffle.