AS MANY as 700 Britons are fighting with Al Qaeda linked extremists in war torn Syria, France’s President Francois Hollande has warned.
He said a similar number from France had also travelled there, making the issue one of the most serious facing his country and the UK.
The two countries have agreed closer cross-Channel co-operation to keep track of potential jihadists. Intelligence services and counter-terrorism experts worry that home grown fighters will return from Syria radicalised and ready to use violence as a means of achieving their goals.
The figure of 700 Britons in Syria is almost double the most recent expert estimate.
The issue - which has become a key focus for the security and intelligence services - was among topics discussed in talks between Mr Hollande and Prime Minister David Cameron in Oxfordshire today.
Speaking at a post-summit press conference, the president said: "We have young people who live in our respective countries who are being manipulated, and they are going off to the combat areas.
"Today we were exchanging figures.
I am not going to teach you anything but it is the same level - 600 to 700 young people are involved in each of our countries.
"So we are going to set up co-operation in order to avoid young people being affected by this propaganda and also be able to monitor their comings and goings and try to prevent this."
Syria is proving a popular training ground with would-be jihadists, with a former head of MI5 warning last year that Britons are increasingly heading to the Middle East for terrorist training in preparation for attacks in the wake of the Arab Spring.
Mr Cameron said: "We have agreed to work together to tackle the security risk posed by UK and French nationals who have travelled to Syria for jihadist fighting and then seek to return here.
"Earlier this month, a defector from the Al Qaeda linked Islamic State of Iraq and al-Sham (ISIS) told the Telegraph that Britons were being indoctrinated in Syria.
The source reportedly said recruits from Britain, Europe and the US were being trained in extremist anti-Western ideology, and told how to make and detonate car bombs and suicide vests. The source said they were then sent home to create new terror cells.
Last week, it emerged two brothers from north London have become the new poster boys for Al Qaeda's holy war in Syria after they were killed in the country fighting alongside Islamist extremists.
Akram and Mohamed Sebah are being hailed as the martyrs and the "Lions of Britain" in recruitment calls from Al Qaeda.
by Ted Jeory