The many hustings that are taking place for the Labour leadership contenders provide excellent arenas for the party and those associated with it to see how the candidates perform, and, more importantly, what they stand for. But there is another test for whoever would be opposition leader: how, and how well, they take on the government. So here's a little idea, probably no more than a bit of Sunday-evening fun.

There are, I think, seven sessons of Prime Minister's Questions between now and the summer recess. There are five contenders for the Labour leadership. Why not allow Harriet Harman, the acting leader, to take this week's and the last before parliament rises, and have each of the five stand in against David Cameron in between now and then?

The only danger is that Cameron would deliberately allow weaker candidates to do better, as what we journalists call a kind of "reverse-spin". As Alastair Campbell's diaries confirm, he and Tony Blair deliberately put it about that it was Michael Portillo they feared for the Tory leadership, when in fact it was Kenneth Clarke. So, you could see Cameron apparently being knocked for six by Diane Abbott. Then again, he probably won't want to be seen to be bested. Anyway, just a thought.