Image copyright PA Image caption Head of MI5 Andrew Parker said the scale of the terrorist threat in the UK was at a level he had not seen in his 32-year career

The head of MI5 has said he is hoping for a mature debate on intercepting communications data, rather than accusations of mass surveillance.

Andrew Parker said the service was not seeking "sweeping new intrusive powers" but rather a framework that "reflects the way that technology has moved on".

He also said the scale of the terrorist threat in the UK was at a level he had not seen in his 32-year career.

A draft bill updating state surveillance powers is due next week.

BBC security correspondent Gordon Corera said Mr Parker's comments, made at the Lord Mayor of London's annual defence and security lecture, was "part of a broader campaign by spies and police to make their case ahead of the new bill".

'Beyond our reach'

Mr Parker used his speech to highlight the need for surveillance powers to be brought in line with modern technology.

"Today the conversations of our adversaries are happening on a bewildering array of devices and digital platforms, often provided by companies based overseas," he said.

"And an increasing proportion of such communications are now beyond our reach - in particular with the growing prevalence of sophisticated encryption."

He said MI5 needed the tools to access terrorists' communications online "just as much as we intercepted written communications and telephone calls in years gone by".

Image copyright Reuters Image caption Mr Parker used his speech to highlight the need for surveillance powers to be brought in line with modern technology

Sifting through large amounts of data - such as phone records - and even hacking into computers was increasingly vital, he argued.

But he said he recognised the need for greater transparency.

Mr Parker stressed that "we do not, and could not, go browsing at will through the lives of innocent people".

He said: "We use these tools within a framework of strict safeguards and rigorous oversight, but without them we would not be able to keep the country safe."

He also said the threat posed by Islamic State militants - also known as Isil - "shows no sign of abating" after more than 750 British extremists travelled to Syria.

Mr Parker said six attempts at terrorist atrocities in the UK had been thwarted in the last year.

"We are seeing plots against the UK directed by terrorists in Syria; enabled through contacts with terrorists in Syria; and inspired online by Isil's sophisticated exploitation of technology," he said.

"It uses the full range of modern communications tools to spread its message of hate, and to inspire extremists, sometimes as young as their teens, to conduct attacks in whatever way they can."