Terror plots escalating in 'matter of days', warns head of M15

Terrorist plots are escalating to the point of violence in a matter of days after a "dramatic" jump in the scale and pace of the threat facing Britain, the head of MI5 has warned.

Andrew Parker highlighted the "short life" of some attack plans as he described how the danger to the UK is now at the highest tempo seen at any point in his 34-year intelligence career.

In rare public comments, he also set out how extremists can exploit "safe spaces" online, making the task of disrupting their activities more difficult.

And he issued a fresh challenge to technology firms, saying they have an "ethical responsibility" to help governments confront the threat.

In his first substantial remarks since Britain was hit by a flurry of attacks this year, Mr Parker detailed the "acute and enduring" challenge posed by Islamist terrorism.

Twenty plots have been foiled over the past four years, including seven in the last seven months.

"We've seen a dramatic up-shift in threat this year," Mr Parker said in a speech in central London.

"Today there is more terrorist activity, it's coming at us more quickly and it can be harder to detect."

Security services and police are operating at a scale which is "greater than ever before", with well over 500 live operations involving around 3,000 individuals.

Agencies must also assess the risk posed by those returning from Syria and Iraq, and the "growing pool" of more than 20,000 people looked at as part of previous terror investigations.