The serving boss of the UK’s home security agency told the Today programme it was becoming more difficult to obtain online information.
Advances in technology are allowing terrorists to communicate “out of the reach of authorities”, head of MI5 Andrew Parker has told the BBC.
He said internet companies had an “ethical responsibility” to alert agencies to potential threats. But MI5 was not about “browsing the lives” of the public, he added.
Ministers are preparing legislation on the powers for carrying out electronic surveillance. Mr Parker, in the first live interview by a serving MI5 boss, said what should be included in new legislation was a matter “for Parliament to decide”.
MI5 boss Mr Parker also told the BBC:
The terrorism threat is the “most serious threat Britain faces in security terms”
Six alleged terror plots have been foiled in the past 12 months, which Mr Parker said was the highest number he could recall in his 32-year career “certainly the highest number since 9/11”
MI5 had to “make choices” about where to put resources, and make sure they were “focused where the sharpest threat is”
On the killers of Fusilier Lee Rigby: “There cannot be a guarantee that we will find and stop everything. That’s not possible. We can’t monitor them all the time.”
He rejected the suggestion that security service tactics can lead to radicalisation saying it was “completely untrue”
He paid tribute to the people who work at MI5 and their work “which so often goes unrecognised”
He said online data encryption was creating a situation where the police and intelligence agencies “can no longer obtain under proper legal warrant the communication of people they believe to be terrorists”.
It was a “very serious” issue, he said, adding: “It’s in nobody’s interests that terrorists should be able to plot and communicate out of the reach of authorities.”
The overall context is a terrorist threat, that MI5 says is growing, technological change and recent concerns over privacy and surveillance.
The question of whether new legislation will maintain existing capabilities against a backdrop of technological change or provide new powers will not be clear until the detail is revealed.
Much of the communications material MI5 needs is held abroad, often by US companies, and he made clear he would like more co-operation from them.
There is recognition from the security and intelligence services that justifying their intrusive capabilities will require more transparency.
That openness may be provided not just by legislation but also by speaking publicly and even coming into a BBC studio.
Mr Parker said the shape of the terror threat had changed “because of the internet and the way terrorists use social media”.
He said they were using secure and encrypted apps and the internet to “broadcast their message and incite terrorism among people who live here”.
The UK’s terror threat is rated as “severe”, which means an attack is highly likely.