LONDON: Britain's security agencies need greater powers to deal with a growing terrorism threat and the advanced technology being used by militants, the head of the country's domestic spy service said on Thursday in the first live media interview by an MI5 chief in its 106-year history.

Prime Minister David Cameron's government plans new laws later this year to bolster surveillance capabilities of spies and police, but faces a battle from privacy and human rights campaigners who say such measures represent an assault on freedoms.

In an interview with BBC radio, MI5 Director General Andrew Parker said Britain was facing its most serious terrorism threat since the Sept. 11, 2001, attacks on the United States and had foiled six attempted attacks in the last year.

"It represents a threat which is continuing to grow largely because of the situation in Syria and how that affects our security," Parker said.

In August last year, Britain raised its terrorism threat level to "severe", the second highest category which means a militant attack is considered highly likely. It was largely due to the danger the authorities say is posed by Islamic State (IS) fighters and the hundreds of Britons who have joined them.

Last week, British police said they had arrested a record number of people on suspicion of terrorism offences, although Parker said his agency was not overly concerned about the thousands of migrants fleeing the ongoing Syrian conflict.

"It isn't actually as we speak today the main focus of where the threat is coming from," he said.

Intelligence chiefs and Cameron have argued for years that the security agencies need more powers to address the threat and prevent another attack on the scale of the London suicide bombings in 2005 when four British Islamists killed 52 people.

OPPOSITION

But moves to bolster surveillance have attracted widespread opposition, including from within Cameron's Conservative party, fuelled in part by former U.S. spy contractor Edward Snowden who has suggested U.S. and British spies are conducting mass monitoring of communications.

MI5 says individuals have been inspired to violence by IS ideology over the internet within weeks, and Parker said he shared the fears of FBI Director James Comey about terrorism suspects "going dark" as spies could no longer legally obtain their communications, making it harder to prevent attacks.

"It's in nobody's interests that terrorists should be able to plot and communicate out of the reach of any authority," said Parker, adding technology and social media companies had an ethical responsibility to come forward if they had concerns about users possible terrorism involvement.

"We're focused on the people who mean us harm," he said. "We're not about browsing through the private lives of the citizens of this country. We do not have population-scale monitoring or anything like that."

Parker also dashed the fantasies of "James Bond" fans, saying MI5 staffs were "basically ordinary people".

"I love the James Bond films because they're so distant from reality we can all enjoy the fiction," he said.