As Britain's terror threat level continues to be at its highest level in several years, the UK's most senior policeman has told Sky News he believes an attack is possible - but unlikely.
In August last year, the Government raised Britain's terror threat level from "substantial" to "severe" because of the threat from militant groups in the Middle East, such as the Islamic State.
In the wake of the Paris terror attacks, Home Secretary Theresa May announced that security would be bolstered at British ports and train stations.
And just days ago M15 chief Andrew Parker warned that the UK faced a threat of "complex and ambitious plots" by extremists .
But in an exclusive interview with Sky, Metropolitan Police Commissioner Sir Bernard Hogan-Howe said the public should remain calm.
"I don't think it's likely but I think we all know it's a possibility - the threat level is severe and so therefore that means a terrorist attack is possible.
"We do our best together with the security services to make sure the terrorists don't succeed and that we keep people safe. To date, that's broadly what we've been able to achieve."
Sir Bernard's primary concern is the hundreds of Britons who have travelled to Syria and Iraq to fight alongside extremist groups, and who could bring that fight back to the streets of Britain.
He says families need to work with the police to prevent their children leaving in the first place.
"The task is to get in there before they go, then we can talk to them and talk to the charities who can help them and persuade them of the foolishness of what they're about to embark on.
"There's no structure in these countries. There is no law. So they only law they've got is the gun. That's the sort of country they're going to."
:: UK Police Anti-Terrorism Hotline: 0800789321