Met Assistant Commissioner Cressida Dick said police forces across the country will have to deal with the threat of British fighters returning from Syria for “many years.”
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 appeared to feature several Britons. The video 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.
One of the men in the video has been identified as aspiring medical student Nasser Muthan, 20, from Cardiff.
Speaking to BBC Radio 4’s The World This Weekend, Ms 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 years.
More than 50 people have been arrested in the UK since 2013 for alleged Syria-related offences. But Ms Dick would not be drawn on the extent to which UK police have already had to confront security threats from British jihadists fighting in the Middle East.
She said: “I’m afraid I believe that we will be living with the consequences of Syria – from a terrorist point of view, let alone the world, geopolitical consequences – for many, many, many years to come.”
Ms Dick said that until a few weeks ago police believed around 460 Britons had gone to fight in Syria, but said the figure could now have climbed to around 500.
She said her message to anyone thinking of travelling to Syria or Iraq to join the fighting was not to go, saying Syrian people regarded foreign fighters as a problem, not a solution.
She said: “I’m afraid I believe that we will be living with the consequences of Syria – from a terrorist point of view, let alone the world, geopolitical consequences – for many, many, many years to come.”
Ms Dick said that until a few weeks ago police believed around 460 Britons had gone to fight in Syria, but said the figure could now have climbed to around 500.
She said her message to anyone thinking of travelling to Syria or Iraq to join the fighting was not to go, saying Syrian people regarded foreign fighters as a problem, not a solution.