The Head of MI5 has warned of a Paris style atrocity by Islamic terrorist groups taking place in Britain.

Speaking at the Royal United Services Institute, Andrew Parker, the Director General of the Security Services, said extremists were “trying to direct terrorist attacks in the UK and elsewhere from Syria”.

And he said that MI5 had “stopped three UK terrorist plots in recent months alone” where deaths would have certainly resulted but warned “Although we and our partners try our utmost we know that we cannot hope to stop everything” and spoke of his concern at the “growing gap” between the threat and the resources security services have to combat them.

Mentioning the horrific attacks in Paris, Mr Parker said it was “too early” to “come to judgements about the precise details or origins of the attack” but warned that it was a “terrible reminder” of what fundamentalists are capable of in our own towns and cities.

He said it would “be surprising” if he didn’t “focus on the ongoing and increasing challenge from Syria”.

“I spoke a year ago of MI5’s increasing focus on this growing threat. It has continued to expand and to morph, not least with ISIL coming to the fore.

“Around 600 extremists are among the many Britons who have travelled there. A significant proportion has joined ISIL.”

Mr Parker said there were three key ways the terror groups were looking to harm British people, the first being “the senseless and brutal murder of innocent Britons in the region.”

“The second” he said, “is that they are trying to direct terrorist attacks in the UK and elsewhere from Syria, using violent extremists here as their instruments.”

“And, third, they are seeking through propaganda to provoke individuals in the UK to carry out violent attacks here.”

Mr Parker said that outside of Iraq and Syria there had been more than 20 terrorist plots with links to extremists in Syria, including the shooting of the soldier in Canada, the hostage-taking at the cafe in Sydney and four people shot dead in Brussels by a French returnee from the fighting.

“We know that terrorists based in Syria harbour the same ambitions towards the UK – trying to direct attacks against our country, and exhorting extremists here to act independently” he warned.

The Security Chief said that ISIL makes full use ”of modern social media and communication methods” which take their messages of hate directly into homes throughout the UK where it can be viewed by those susceptible to their propaganda.

He said it was the widespread use of the internet which led the government to bring forward fast track legislation on data retention and investigatory powers and said that Parliament and society will once again need to look at the balance between necessary tools to combat the threats we face and intrusion into people’s lives.

Mr Parker warned that the number of “crude but potentially deadly” plots has risen, using Canada and Australia last year as examples. “Such attacks” he said “are inherently harder for intelligence agencies to detect,” words which will be used by those in government who want internet companies to become more involved with the government and its agencies in dealing with potential terror attacks especially in the light of the report into the murder of Lee Rigby.

But Mr Parker said that with spontaneous attacks, it was often down to friends and family or members of the public to notify the authorities about individuals moving in a concerning direction towards extremism or violence.

“2015,” he said, “we will need more help from the public in these sorts of situations. Such assistance will be invaluable when it comes to enabling MI5 and the police to save lives.”

At the same time, he warned that a “core” group of Al Qaeda terrorists in Syria “is planning mass casualty attacks in the West.”

With the manhunt for the killers of the Charlie Hebdo staff and police officers, the message from security forces is that danger is all around.

And while they have to get the situation right every time to prevent an attack, terror groups or lone individuals who have been brain washed by extremism streamed into their computers at home, they only have to get it right once to cause death, injury and fear.