Sean O'Grady: As Harman attacked, Cable turned into Osborne's poodle

A parallel universe in which the Conservatives squeaked home to a narrow parliamentary majority is not so difficult to imagine. The Liberal Democrats – slightly fewer than now – would be sitting on the opposition benches and their response to the Budget would have been rather different.

After George Osborne and Harriet Harman had finished, Nick Clegg would have risen in the Commons, the place would have emptied as usual and, in that reasonable way of his, he would have acknowledged the scale of the fiscal crisis. But he would also have joined Labour and slammed the Tories for attacking the most vulnerable; for panic cuts that threatened long-term growth and for taking the "risks with recovery" that we heard so much about in the campaign. The Tories' "secret VAT bombshell" predicted by the Liberal Democrats before the election would have been seen to have exploded, with Mr Clegg ready to bemoan the wreckage.

The rise in VAT would have been condemned as unfair and regressive, as Simon Hughes, the Liberal Democrats' new Deputy Leader, has said. The assault on public services would have been resisted.

Though Mr Clegg and Vince Cable have done their best to reform their party, it remains heavily biased towards public sector interest groups in education and health and the party's local government base is an obvious focal point for dissent about cuts to local authority spending. Mr Clegg would also have sensed that the Tories' danger is the Liberal Democrats' opportunity.

Every Liberal revival since the war has been at the expense of an unpopular, Conservative administration. In this parallel world, a run of by-election and local election wins from now to 2015 would glint brightly across the political landscape. For all sorts of reasons, then, Mr Clegg would have savaged Mr Osborne.

Things are not like that, though, and Liberal Democrats may be starting to feel ever more uneasy about what is happening around them, and to them. They might have winced as Ms Harman tore through them and noted Mr Cable's transformation into Mr Osborne's poodle, which must have hurt.

I take as my reference point the Liberal Democrat MP, Bob Russell. Mr Russell is no one's idea of a British Obama, but then again he has no pretensions to such. He is simply a decent Liberal Democrat, doing his best for the people of Colchester. In his way, he is typical – and he has said that his "principles and conscience can't be parked elsewhere".

"I supported the formation of the coalition through gritted teeth but I have never voted for big cuts in welfare and I am not going to start now."

We can assume he'll be otherwise engaged when the whips want him to vote for the freeze in child benefits.

No wonder, then, that Mr Clegg felt compelled to write to his party members, appealing for some forbearance. The other day I, too, received a letter from Nick Clegg, as a "Lib Dem supporter". He asked me to focus on what the coalition was doing that would not be happening if it was a purely Conservative administration – in particular to the pledge to take anyone on less than £10,000 out of income tax.

That, and that alone, is why most Liberal Democrats will be sticking with this Budget. But as Mr Russell intimated, there has to be more to this coalition than that.