David Cameron made an admirably provocative statement as he tried to defend his handling of the Maria Miller affair: “This is a good and honest Parliament with good and hard-working people in it.”

Many people will at once reject this assertion. There is a widespread view that MPs are a bunch of greedy and corrupt scoundrels. It seems unlikely this will become known to history as the Honest Parliament. The names we have given to particular Parliaments have most often been uncomplimentary: they include Addled, Barebones, Drunken, Dunces, Mad, Mongrel, Rump, Unlearned and Useless.

The Prime Minister agreed that the anger about MPs’ expenses “is still very raw”, and urged the House to “do more to reassure the public about our handling of expenses”. But his manner conveyed an underlying sense of moral indignation: he feels it is wrong to assume that MPs are corrupt. Cameron did not actually say he stuck to Miller for so long because he thought she had done nothing wrong, but that was the implication of his words.

So there was Cameron entrenched on the moral high ground, defending the conventional view that MPs are honourable: a view which centuries of parliamentary practice have shown is necessary, even if it is not always strictly true.

Ed Miliband had not worked out what to say to this. He accused Cameron of making “a terrible error of judgment” in not sacking Miller sooner. But Cameron’s case was that he had no right to rush to judgment: rather than assume a minister is guilty, one should look carefully at what is being said and see whether that individual in fact deserves to be given the chance to carry on.

Some cases are, of course, open and shut: it is at once clear that things are so bad the minister must resign. But if this was one of them, why did Miliband not call on Miller to resign?

Cameron put that question to Miliband, who naturally declined to answer it. He rightly insists that it is not his job to answer questions. But it is his job to oppose the Government, and this he yet again failed to do.

The best way for Miliband to oppose on this occasion would have been to make statesmanlike proposals for reform, the effect of which would have been to make Cameron to look small and inadequate. Miliband would have emerged as the true leader of Parliament, the man who knows how to re-establish the integrity of that institution in the eyes of the nation.

But it is much easier to see the desirability of statesmanlike measures than to know what they would be, and Miliband could shed no light on this question. His leadership style recalls the Duke of Plaza Toro, who “led his regiment from behind – he found it less exciting”.

The Prime Minister chose a different analogy. He dismissed Miliband for attempting to jump on the bandwagon “after the whole circus has left town”. And there, sitting on the front bench, was Sajid Javed, the new Culture Secretary. The Government has moved on, leaving Miliband behind.

This could have been an excruciating PMQs for Cameron: the day when the many people who deeply dislike him rejoiced to see him humiliated. But although Cameron sounded resentful, he did not look like a Prime Minister whose authority has been shot to pieces. How fortunate for him that Miliband is the Leader of the Opposition. Tony Blair would have had a field day.