Security expert: 'Difficult to manage the numbers'published at 16:22 British Summer Time 6 June 2017
The World at One
BBC Radio 4
Richard Barrett, a former head of counter-terrorism at MI6, has told the World at One that a "sophisticated amount" of co-operation between security services is required to enable them to manage the volume of potential suspects travelling between countries.
The London Bridge attackers were "known to security services" and Mr Barrett says the difficulty is the volume of people who need monitoring and also the speed at which someone moves from being radicalised to taking action, which he says has changed from "years to possibly a matter of months or weeks".