7/7 bombing anniversary: MI5 chief warns Britain faces a 'serious societal and security challenge' from some of its own citizens

Andrew Parker says atrocity is 'enduring reminder' of what his organisation 'is striving every day to prevent'

An image taken from CCTV footage of three of the four 7/7 bombers. From left to right: Mohammed Sidique Khan, Germaine Lindsay and Shahzad Tanweer arriving at King's Cross (Getty)

Britain faces a “serious societal and security challenge” from some of its own citizens who are prepared to target their homeland, according to the head of MI5.

Speaking on the eve of the tenth anniversary of the 7 July 2005 London attacks, Andrew Parker said “individuals who have grown up here but decided for whatever twisted reasons to identify their own country as the enemy,” were “a tiny fraction of the population.”

“But the continuing fact that some people, born in the UK, with all the opportunities and freedoms that modern Britain offers, can nonetheless make those sorts of warped choices presents a serious societal and security challenge,” he said.

The “shocking and brutal” murder of holidaymakers in the Tunisian beach massacre has “yet again brought the reality of terrorism to the fore”, he added.

In this country, he said the “disgusting” 7/7 attacks - in which a series of coordinated suicide bomb attacks in the central London rush hour claimed the lives of 52 civilians and injured 700 more - served as an “enduring reminder” of what his organisation “is striving every day to prevent.”

That day a decade ago had ended any doubt about the danger facing the UK and led to a ”step-change“ in the nation's counter-terrorism defences which was crucial in foiling future plots, he said.

“A year later we detected and with partner agencies, prevented al Qaida's most ambitious plot to bring down multiple airliners on US cities using liquid bombs on flights from London,“ he added. ”Thousands would have died.”

However, Mr Parker, who had taken over as counter terrorism director a few months before the 7/7 said: “We could not have prevented 7/7.”

“We had always known and said publicly we simply can't find and stop every terrorist plot,” he said, adding: “While it remains true that we thwart most attempts, the rare occasions when terror attacks occur stand as stark moments in contemporary history.”