Donald Macintyre's Sketch: Shameless PM fails to persuade MPs he is serious with his dodgy tackle

At last, we understand. All that stupid, ill-informed speculation that Michael Gove – or “the former Education Secretary” as David Cameron described him today, the phrase slipping with surprising ease from his lips – had been demoted.

It was simply, as he explained, the need to find “the best candidate for the job” to replace Sir George Young, an “extraordinary politician” of 40 years’ standing who had “served the country so well as Chief Whip” and would soon leave Parliament.

Sir George, who to his permanent credit led the Tory rebellion against the poll tax, does indeed have an impeccable public service career behind him. Even if his last job is normally thought to be more useful to the party than “the country.”

But Cameron, who hardly kept a straight face as he unveiled this crazily improbable back-story, cannot have thought anyone would actually believe that no one else could do the enforcer job in a pre-election year when the chances of a serious parliamentary rebellion are exactly nil.

Labour’s Pat McFadden asked how Cameron would ensure that Lord Hill (whom no one in Brussels has heard of) got a top European Commission job. For some reason Cameron didn’t answer, as he might have: “Look mate, we’ll do our best, but if you think I was going to risk a by-election by sending an MP there you must be mad.”

And Jack Straw asked “what possessed” the PM to sack Dominic Grieve (who has been a bit of a stickler for the – by Tories – hated European Convention of Human Rights) when it was the Attorney General’s job to “speak legal truth to power”.

This might seem a bit rich given lingering doubts over whether Tony Blair’s Attorney General Lord Goldsmith quite did that over Iraq. But it was a good point, hardly met by Cameron’s answer that when “someone has served extremely well for four years, there are often times when it is right to…” What? Sack them? No. “…bring on new talent.”

But then shameless was the Prime Ministerial order of the day. Ed Miliband had earlier been doing OK, taunting him about Gove and coming back at yet another fall in unemployment figures, arguing that the recovery meant little to “people, who are working harder for longer for less”.

But then Cameron triumphantly produced a Harriet Harman quote from an LBC phone-in: “I think people on middle incomes should contribute more through their taxes.”

Ecstasy on the Tory benches! Miliband tried bravely to shrug the supposed gaffe off, saying that “this is totally desperate stuff”. But the tide had turned; the Tories noisily willed Cameron on to his show closer: “in this party the leader reshuffles the Cabinet; in his party, the shadow Cabinet desperately wants to reshuffle the leader”.

Except this was the Prime Minister’s Questions’ equivalent of the (very) dodgy tackle. Cameron had accused Labour’s Deputy Leader of revealing “its policy to put up taxes on middle-income people”.

But Harman had done nothing of the sort. All she had done was defend at some length the fact that – now – middle-income earners pay more tax than the poorest. Which since the Coalition always boasts of having taken the lowest earners out of tax is hardly controversial.

Of course, it worked on the pitch, as professional fouls often do. But if this is a taste of the coming election, heaven help us.