Boris Johnson and Keir Starmer know that the stakes are high ahead of their first PMQs clash

The mind games may have already begun as the prime minister looks to keep the Labour leader guessing, writes John Rentoul

Sir Keir Starmer, left, is likely to face Boris Johnson at the despatch box at PMQs for the first time (PA)

It says something about the forthcoming Prime Minister’s Questions that Boris Johnson’s official spokesperson wouldn’t confirm in advance that the prime minister would actually be taking part in it.

I assume this was a tiny tactical device designed to keep Sir Keir Starmer guessing as to whether he would be facing his principal opponent for the first time at noon tomorrow, or his substitute, the foreign secretary. It is the equivalent of sledging: trying to put your opponent off.

The prime minister could pay no higher tribute to the new leader of the opposition. Why play such games unless Johnson thinks that he is up against an opponent who poses a threat to him?