Armed police outside the Houses of Parliament during the attack in Westminster in March © Reuters
Andrew Parker, the head of MI5, said the UK was facing the “highest tempo” of threats in more than three decades, as Britain’s intelligence services and police race to tackle a “dramatic upshift” in the threat of attacks from Islamist extremists.
The UK has been hit by several terror attacks this year, with 36 people killed in Manchester, Westminster and London Bridge. Last month 29 people were injured when a homemade bomb left on a tube train partially exploded at Parsons Green station in west London.
The UK’s terror threat level was briefly raised to critical before being reduced to severe, where it has remained since September 17, meaning an attack is highly likely.
In a rare briefing for journalists in central London, Mr Parker said that MI5, the UK’s domestic security service, had foiled seven plots intended to “maim and kill in Great Britain” since March and 20 since 2013.
“We have seen a dramatic upshift in threat this year,” said Mr Parker. “It’s at the highest tempo I have seen in my 34-year career.
“It’s clear we are contending with an intense UK terror threat from Islamist extremists. That threat is multi-dimensional, evolving rapidly and operating at a scale and pace we have not seen before.”
Mr Parker also revealed that there had been 379 terror-related arrests in the UK in the year to June — a record number — and that there were over 500 live operations involving around 3,000 individuals “involved in extremist activity”.
A further 12 terrorists had been arrested and were being held in mainland Europe following joint intelligence operations with the UK’s European partners.
As Islamic State fighters retreat from strongholds in Syria and Iraq following sustained pressure from US-backed forces, Mr Parker said it was unclear what risk may be posed by the estimated 800 British jihadi fighters who have travelled to the region from the UK.
“We haven’t yet had a large influx of returnees,” said Mr Parker. “Some will simply never want to come back at all and may try to move on to other areas.”
Following this year’s terror attacks in Britain and Europe, technology companies like Facebook, Google and YouTube have come under growing pressure from politicians to take tougher measures to crackdown on extremism online.
Earlier this month, UK home secretary Amber Rudd announced that, in a widening of the laws to tackle radicalisation, people who stream and repeatedly view terror content on the web could face up to 15 years in jail.
In Germany a new law means tech companies will face fines of up to €50m if they fail to remove obviously illegal content within 24 hours.
The technology groups say they are stepping up to the challenge. Twitter reported recently it had suspended 300,000 accounts linked to terrorism in the first half of 2017 and YouTube and Facebook are increasing the use of artificial intelligence to detect and take down extremist material.
Highlighting for the first time online shopping platforms that may help terrorists assemble homemade bombs, Mr Parker said all technology companies had an “ethical responsibility” to help tackle the “unintended side effects” and “dark edges” of the web.