We think of spy swaps as being thoroughly and always unscrupulous, but there actually are rules of the road. There is a protocol between the two intelligence agencies, a sort of honour among thieves. That's why it's very odd to see somebody like Skripal, being targeted like this. And until we have some forensic evidence – and proper circumstantial evidence – it's premature to accuse the Russian government of having been involved.
It does seem that Skripal was involved in something: likely to be something to do with his stock-in-trade – which is the exchange, the buying and selling of information. And when you do that, you sometimes work with unscrupulous economic actors, who may be on the dark side.
The fundamental problem from the British perspective is that we opened up London to all comers. Very few questions were asked about where their money was coming from. And that remains the same today, because people can still come from outside the country and use anonymous companies to buy up property and businesses. London is attractive for Russians because it is only a four hour flight from Moscow, we speak English, you can send your kids to good schools. But if they felt the British were going to come in and do something about this money, you would see it be whisked away overnight to somewhere else. There are always places to hide this stuff.
The Litvinenko case was very drawn-out. We had a tough response initially; that was, of course, under a Labour government. There was a bit of flip-flopping when Theresa May was Home Secretary. But the fundamental problem for the British is that we already impose a whole raft of sanctions on Russia - along with the EU and the US - so what else are we going to do?
This is an edited transcript from Misha Glenny's interview on Radio 4's Today programme