GEORGE Osborne has made clear that Britain's security forces will get all the resources they need after the head of MI5 warned that there was a "growing gap" between the terror threat facing the country and the capabilities available to the security services.

Andrew Parker said a group of core al Qaeda terrorists in Syria was planning "mass casualty attacks" against the West, including the UK, in a stark reminder that the threat to this country continued to stretch beyond the militants of the Islamic State.

But the Chancellor stressed how the UK Government had ploughed a "huge amount of planning and effort from the police, from the security services, from the Government, into anticipating what might happen, stopping some of these attacks".

"Of course, we have been successful in doing that over the last year," he said.

Mr Osborne explained how within the last few weeks more than £100 million had been put into monitoring "self-starting terrorists" who were going to conflicts in Syria and Iraq, getting their ideas off the internet and then wanting to perpetrate horrendous crimes.

He added: "My commitment is very clear: this is the national priority, we will put the resources in, whatever the security services need they will get because they do a heroic job on our behalf."

The Prime Minister's spokeswoman said David Cameron was committed to ensuring that the security agencies could deal with the "evolving" threat of terror but she declined to say specifically if there would be any new legislative changes on giving the authorities more control on intercepting communications.

"The PM thinks it is vital that we do all we can to support the police and agencies to tackle the increased threat of terrorism and to make sure they have the resources and powers that they need," she said.

Sir Malcolm Rifkind, who chairs the Intelligence and Security Committee , said the Paris attack had given "added weight" to the case for intelligence services being given stronger powers to intercept communications.

It had become "increasingly difficult" to access vital evidence, he said, noting: "What is emerging in Paris is that the two individuals responsible for the terrible massacre at Charlie Hebdo may have been linked to al Qaeda in the Yemen. They must have been communicating with people in the Yemen over the last few days, the last few weeks."

The former Foreign Secretary said it was hugely important to enable intelligence agencies in Britain and France and other democracies to be able to get hold of these communications to try and prevent incidents of this kind.

"It gives added weight to the point that in a realistic world, if you are dealing with international terrorism, how do international terrorists communicate with each other? In the modern world they communicate through the internet, through email, through social messaging and all the technical ways that we are aware of. So our intelligence agencies, acting under law, acting on good reasonable grounds, with authority, have to have the power to intercept particularly international communications that might be relevant," he added.