Sir John Sawers stepped down last year after five years as chief of the UK Secret Intelligence Service, MI6, a post known as 'C' in the service.
He was the first MI6 chief to be chosen from outside the service for 41 years and oversaw the security arrangements for the Olympic Games in 2012. Sir John, 60, is a career diplomat who has also worked as the UK's ambassador to the United Nations, political director of the Foreign Office, special representative in Iraq and a policy adviser to Tony Blair when he was Prime Minister.
But he was no stranger to the world of espionage, having trained with MI6 at the start of his career before joining the FCO.
Today, in an interview on CNN's Global Public Square, he said the risk of a terrorist attack hitting the West has grown substantially since he stepped down from the role.
He said: 'We were pretty confident that the London Olympics would be terrorism-free. And thanks to a lot of hard work, it was.
'I don't think you could be quite so confident now if the London Olympics were in 2016, for example.' Sir John said the way terrorists carry out their heinous attacks has changed drastically since the emergence of ISIS.
'They're not trying to fly airliners into buildings. They're doing simpler things,' he said.