A Government minister has issued a new appeal to the public for vigilance in the face of the continuing terrorist threat.
Security Minister Ben Wallace said that if people saw signs that those they knew were becoming radicalised, they should report it to the authorities.
He called for a return to a mindset of the 1970s and 1980s where people were on the lookout from the threat of the IRA bombing campaign.
His comments follow a warning from the former head of MI5 Lord Evans of Weardale that the current threat of Islamist terrorism could persist for another 20 or 30 years.
Mr Wallace said the speed with which people could move from being radicalised online to carrying out deadly attacks meant it was vital that the public stayed alert.
"This is why the Government is very keen to make sure that this is not just about the intelligence services and the police. It has got to involve all of us," he told the BBC Radio 4 Today programme.
"We have a really strong role to play in this, especially with that group of what we would call 'sudden violent extremists' – people who just may live next door that the police will not necessarily have time to get to," he said.
"If we see something suspicious, if we are worried about things, we should raise the alarm.
"We have got to get back to that stage which we had in my childhood where the IRA had bombing campaigns in the mainland. We looked out for things. We always asked ourselves 'Is that a suspicious thing?' and did something about it.
"I think that is where we have to get to again, especially with people who could very, very quickly be radicalised and take lethal action."
Mr Wallace said the Government was also determined to ensure that the big internet companies such as Google and Facebook did more to take down extremist material.
"We are as a Government exploring a range of issues that we can look at ranging from whether we have existing legislation or whether there is a requirement for new legislation, all the way through whether there is new technology that we can incentivise these companies to put in place," he said.
"They absolutely have a duty to do something about it. Our biggest concern is that safe spaces are where everyone from paedophiles to terrorists are sitting using things such as encryption to carry out their awful, awful practices.
"We have to do something about it. We cannot sit back and let it ride."