The head of MI5 has warned that terrorist plotting against Britain is at its most intense for three decades and still growing as he backed new powers to monitor communications.
Andrew Parker said new technology was posing ever-greater challenges to his agency as he argued that internet firms such as Facebook and Twitter had a “responsibility” to share information.
But he stressed that MI5 was not interested in “browsing through the private lives” of the general public and should work within a “transparent” legal framework.
Giving the first live broadcast interview by any security service chief on BBC Radio 4’s Today programme, Mr Parker played down fears about extremists entering Europe among the stream of refugees from Syria.
He said the police and security services had intervened to foil six terrorist plots in the UK over the past 12 months and the threat was growing.
“That is the highest number I can recall in my 32-year career, certainly the highest number since 9/11,” he said.
“It represents a threat which is continuing to grow, largely because of the situation in Syria and how that affects our security.”
Mr Parker said the “shape” of the threat was changing dramatically. “They are using secure apps and internet communication to try to broadcast their message and incite and direct terrorism amongst people who live here who are prepared to listen to their message,” he said.
The MI5 chief said the agency was focused on monitoring “where terrorists may be and how they are moving”.
He added: “As far as the flow of migrants and refugees go, of course it is something we are aware of.
“It is not actually, as we speak today, the main focus of where the threat is coming from.”
Mr Parker set out the challenges facing the security services as the Westminster government prepares for a battle over legislation dubbed the “snooper’s charter”.
The Investigatory Powers Bill would oblige UK internet service providers to keep data on their customers and make the information available to authorities.
Mr Parker said: “Because of that threat we face and the way the terrorists operate and the way we all live our lives today, it is necessary that if we are to find and stop the people who mean us harm, MI5 and others need to be able to navigate the internet to find terrorist communication.
“We need to be able to use data sets so we can join the dots, to be able to find and stop the terrorists who mean us harm before they are able to bring the plots to fruition.
“We have been pretty successful at that over recent years, but it is becoming more difficult to do it as technology changes faster and faster.”
He reassured people that MI5 was not interested in their private lives.
“The important thing to say is that we focus on the people who mean us harm. We are not about browsing through the private lives of citizens of this country,” Mr Parker said.
“We do not have population-scale monitoring or anything like that.”
Mr Parker insisted he did not “have a view” on specific measures such as whether ministers or judges should authorise interception of communications, insisting it was “not for me to say what should or should not be in that bill”.
But he said it was important the law was updated so it was “modern and transparent” and “describes as straightforwardly as it can what MI5 does these days”.