Activity by counter-terror police is at its highest level for nearly ten years due to fears that Islamic State sympathisers will launch attacks in the UK.
The Times reports that police are increasing armed patrols and are searching homes and cars, while also monitoring extremists who have returned from fighting in Syria.
The stepping up of security comes after the release of a video showing an unmasked British jihadist urging “all brothers in the UK” to seek revenge for British air strikes against the self-proclamed Islamic State.
Addressing Muslims who cannot make the journey to Syria and Iraq, the militant says: “Unlike us, you are blessed in that you can cause terror in the hearts of the kufar [non-believers], right in the centre.”
“You can cause terror right from within,” he adds.
The Times says that the number of police searches shot up in the space of a month, from 15 in July to 68 in August, and that the rise corresponds to the raising of the terror threat level to “severe”.
Counter-terrorism researcher Olivier Guitta told the paper that the threat of an attack on British soil has risen ten-fold since Britain joined US-led air strikes against Islamic State. “They should be very worried not only of returning jihadists but of people who are here. They will say, ‘I am not going to go all the way to Syria, I can just do it here’.”
London is the British city that is most vulnerable to attack, with numerous jihadists having been recruited from its population, including the masked man who has beheaded a succession of hostages in gruesome videos released online.
The killer, whose name is now believed to be known by security services is now the subject of intense scrutiny, and has threatened to kill yet another hostage.
It is not known whether Western powers will attempt a rescue operation, as such action could be extremely difficult and dangerous. Lord Richards of Hertsmonceux, former head of the British Armed Forces, said this weekend that a rescue would be “very, very difficult”. He told BBC One’s Andrew Marr Show: “As good as the SAS [British special forces] are, they also are — very rightly — very cautious, and I think to expect them to do that is a tall order.”