David Cameron is not ruffled at all by Jeremy Corbyn. Oh no, definitely not.

Many Tory MPs insist, Mr Corbyn is their dream Labour leader.

They are all absolutely delighted that he has been elected.

So why does it appear that Mr Corbyn is getting under the Prime Minister’s skin?

It could be the effect of sheer repetition. Mr Corbyn picked up at Prime Minister’s Questions (PMQs) exactly where he had left off last week.

Ah, I hear you cry, which of that session's six questions did he repeat? All of them. In one.

The veteran left-winger last week famously asked the Tory leader six times if people would be worse off through tax credit cuts under his government.

Mr Cameron dodged the question every one of the six times.

And yesterday he so again, making it seven.

But he appeared to be getting riled by the Labour leader and, indeed, the whole process.

At one point he snapped at Mr Corbyn that when it came to the impact of tax credits he could “find out in three weeks”.

The Islington MP rather swiftly picked him up on another suggestion that their confrontations were ‘entertaining’.

Serious issues around real people’s lives were not designed to be entertaining, Mr Corbyn told the Prime Minister.

Mr Cameron could be seen gulping a swig of water from the glass in front of him at that one.

Later he delighted his own backbenches by hitting out at a question about a war veteran’s finances, telling the Labour leader that if it was up to him serving soldiers would be on the dole.

He was also in a more conciliatory mood when SNP leader Angus Robertson criticised the Tory government’s record on the military covenant, saying he would see what more could be done.

Later, however, he suffered every politician’s nightmare when he was picked up by a microphone whispering to the Speaker as he left the chamber.

The sessions were getting “longer and longer”, Mr Cameron moaned.

Which is, of course, true. The half an hour that is PMQs now regularly last 35 or 36 minutes and on one occasion a few weeks ago even touched 40 minutes.

But, of course, politicians are not supposed to complain about these things.

Especially those who insist that they are not at all bothered by the new leader of the opposition.