London: The UK will have to deal with the threat of British fighters returning from strife-torn Syria for "many years", a top Scotland Yard officer warned today.
Metropolitan Police Assistant Commissioner Cressida Dick said the Syrian conflict represented a "long-term" terrorist threat.
She said young British Muslims might commit violence on their return. Her comments came after an apparent internet recruitment video for jihadists in Syria and Iraq featured several Britons.
The film was posted by internet accounts linked to militants from the Islamic State of Iraq and the Levant (ISIS), which has a presence in Syria and is engaged in fierce fighting with Iraqi government forces.
Speaking to BBC Radio, Dick - who is currently head of specialist operations including counter terrorism at the Met - warned Britain would face "the consequences" of the conflict in Syria for "many years to come".
"We are really alert to the fact that people may come back and they may have military training," she said.
"They may seek - although it`s very difficult - to smuggle weaponry here and they may seek to cause violence or to encourage others to cause violence.
She said until recently police believed around 460 Britons had gone to fight in Syria, but said the figure could now have climbed to around 500.
"It`s very difficult to know absolutely who has travelled or where they currently are," Dick said. "I don`t think anybody will ever have an absolutely definitive number."
Former MI6 director of global counter-terrorism Richard Barrett told Sky News that as many as 300 radicalised young men had already returned to the UK.
Barrett said it was an "absolute nightmare" for security agencies because they do not have the resources to track all of them.
More than 50 people have been arrested in the UK since 2013 for alleged Syria-related offences. Britain on Friday banned five Syria-linked jihadist groups, including the ISIS, making it an offence to be a member of any of the groups in the UK.