by Michael Dugher

At last week’s prime minister’s questions, David Cameron was asked a very specific question by Ed Miliband. Namely, “when the prime minister signed off his welfare bill, did he know that it would make 7,000 cancer patients worse off by as much as £94 a week”?

Cameron denied that this was the policy, replying that this was “simply not the case”, when of course it jolly well was the case. As Ed Miliband continued to batter away at the prime minister, it was blindingly obvious that Cameron did not have the faintest idea what was in the bill that was before the House that very day. Not for the first time, it exposed the fact that David Cameron doesn’t do detail.

One of Cameron’s more desperate comments last Wednesday, was to say to Ed Miliband that he should “check his facts before he comes to the House”. But by the afternoon, Downing Street and the DWP were confirming that the government were pressing ahead with plans to remove out of work benefits from people with cancer if they don’t find work within a year. No 10 said it would not be making any changes to the bill that might provide exemptions for cancer patients.

Cameron is usually an assured Commons performer. He is rarely short of self-confidence (expensive public school education instils this in people). But Cameron, like so many Conservatives, also believes that he was “born to rule”. As such, his performances in Parliament can be breezy, he is light on his feet and has an easy manner in the chamber. He has also improved with experience.

But his over-confidence is his greatest weakness. You get the impression that he never bothers to do his homework. Labour members complain that the prime minister rarely answers their questions. I am convinced that one of the reasons for this is that he simply doesn’t know the answer.

This is not the first time that Cameron has failed to have a grasp of detail. Only a few months ago, he got his facts wrong on the number of black students studying at Oxford university. He also famously accused two private schools of being established by an “extremist Islamist foundation”, which later turned out to be completely unfounded. Another clanger was his confident assertion that Iran has already “got a nuclear weapon”. And last year he appeared to belittle the efforts of British veterans by saying that the UK was the “junior partner” in the allied fight against Germany in 1940, neglecting the fact that the US didn’t enter the war until 1942.

There are further examples. Cameron was caught out in an interview with the Gay Times before the election. It became apparent that he was unaware that his Tory MEPs had abstained on a vote about a motion to condemn a new homophobic law in Lithuania.He also appeared unable to say if Tory peers would get a free vote on a Lords move to allow civil partnerships in places of worship. At one point during the interview he asked, “can we stop for a second”? How he must have wished he had been able to say that to Ed Miliband during the PMQs last week.

Labour shadow minister Ian Austin, who was a parliamentary private secretary to Gordon Brown when he was PM, and was often involved in preparations for PMQs, said to me last week: “can you imagine Gordon Brown, Tony Blair, John Major or Margaret Thatcher not knowing about a key measure in their own reforms”?

Prime ministers spend hours in the cabinet room at No 10 preparing for PMQs. In truth, when you think of all the important things that prime ministers could be spending their time doing, they probably spend too long being briefed for one 30 minute parliamentary set-piece. But the public are right to expect that the person in charge of their government has at least a vague idea about what is going on in the government. Similarly, prime ministers ought to think through their reforms very carefully before they introduce them.

But the truth is Cameron does not think things through. His government is not only callous, it is careless. This is one of the reasons for the abundance of u-turns of late. Cameron may well be being urged to work rather harder at mastering some of the detail of his own government’s policies, not least after his mauling by Ed Miliband last week. Certainly Labour should use prime minister’s questions to find out what David Cameron knows what is going on in his government. To quote Paul Daniels’ famous catchphrase, I suspect the answer might be “not a lot”.

Michael Dugher is Labour MP for Barnsley East, a shadow minister and parliamentary private secretary to Ed Miliband.