Dr Julian Lewis: I speak not only as a former member of the ISC, but as someone who was involved in the 1980s in trying to counter what were called active measures – the use by the Soviet Union of agents of influence and organisations to try to have an impact on British public opinion. The difference between then and now is that it was then quite easy to expose who was behind the influence operations, but now that is much harder because the internet allows concealment.

Does the right hon. Gentleman [Liam Byrne] agree that one of the main antidotes to the concerns expressed in this debate is that the intelligence agencies, and particularly the new technological arm of GCHQ that deals with the internet, should work to expose who is behind the messages that are coming through? We cannot stop messages getting through, but we can neutralise them by showing up their provenance.

[Liam Byrne: The right hon. Gentleman is exactly right. There are well-sourced reports that there have been at least two briefings about Russian interference to the Prime Minister, if not the Cabinet. It is not clear what action was taken in response, but it is now quite clear that dark forces have new techniques. We recognise their fingerprints in some of the referendums and elections that have played out in our country and elsewhere, but let us be under no illusion that their job is not done. They will continue to try to influence debates in this House because they want to change the political environment in which we debate the terms of Brexit, for example. The faster the ISC can do its work and expose, in an appropriate way, what is truly going on, the better for all of us.]