Dr Julian Lewis: Does the Prime Minister recall that when Edward Heath expelled more than 100 Russian so-called diplomats in the early 1970s, it gave a blow to Russian intelligence operations against this country from which it did not recover until the end of the Cold War? Does she also recall that when it was clear that a member of the Libyan Embassy staff – which one was unknown – had killed WPC Yvonne Fletcher, a wholesale expulsion of staff occurred then? As it would be impossible for an operation to have been mounted by the Russian state without someone in the London Russian embassy knowing about it, does she therefore conclude that similar measures may well be necessary?

[The Prime Minister: I thank my right hon. Friend. As I said in my statement, my right hon. Friend the Foreign Secretary has called the Russian Ambassador into the Foreign and Commonwealth Office today and presented the two possibilities of the origin of this action to him. We wait for the Russian State’s response. I am very clear that, should that response not be credible, we will conclude that this action is an unlawful use of force by the Russian State against the United Kingdom, and as I said earlier, I will come back to the House and set out the full range of measures that we will take in response.]