It is estimated that there are 500 British jihadists in the terror groups now operating in the Syrian and Iraqi theatres of war. They are said to be among the most vicious and dedicated fighters in organisations like Islamic State, having carried out horrific acts of violence, and some even becoming suicide bombers.
But to date these reports have made little more than a passing impact on the public consciousness in the UK. That all changed yesterday with the beheading of American photo-journalist James Foley by an Islamic State terrorist speaking with a British accent.
It is now accepted that the terrorist is British and intelligence services in the UK and America are desperately trying to identify him.
The execution of Mr Foley was videoed and posted online with the warning that further killings would follow if America continued to use its air power to bombard Islamic State fighters, who are seeking to set up a Muslim superstate in the Middle East.
The fact that David Cameron broke off his holidays to chair emergency meetings with the intelligence services and other advisers shows the alarm caused by this act. The great fear is that more British nationals will join the Middle Eastern terror groups and that they and the existing hardened fighters will import their violence back into Britain.
Up to this point a lot of effort has been put into working with peaceful Islamic groups – and they are in the vast majority in the UK – to identify and nip in the bud any potential terror plots or would-be terrorists.But it is clear from the large numbers of jihadists who have gone from the UK to the Middle East that this approach is not working as well as hoped for. Perhaps the intelligence services should look towards Northern Ireland and see how dissident groups here have been infiltrated and their operations compromised and adopt a similar tough approach with Islamic extremists in the UK.
The horrific murder of Mr Foley is certainly a wake-up call that cannot be ignored.