Sir Peter Fahy, Chief Constable of Greater Manchester Police, told the BBC on Saturday that there was "huge concern" that Britons arriving back after fighting in Syria posed a threat to the UK.
This month 16 people have been arrested on suspicion of terror offences after travelling between Syria and the UK. This compares with 24 in the whole of 2013.
A Metropolitan Police spokesman said some of those going to Syria to train in terror camps or fight were as young as 17, and that the majority were young men - although they were aware of some young women also travelling there.
According to BBC, Sir Peter, who leads the Association of Chief Police Officer's "Prevent" strategy on counter-terrorism, said that those returning from Syria "may well be charged and investigated, but they will be put into our programs".
"Clearly we've got all sorts of ways of trying to establish that [they have been to Syria]. We have links with intelligence agencies across Europe.
"This is a very difficult situation because Syria is so close. It is very close to tourist destinations, but it is an incredibly dangerous place."
He said those stopped at the border were put on programs - which saw police work with local agencies such as schools and youth organizations, "essentially to make sure these people haven't been affected and try and make sure they're not a threat to this country".
Sir Peter continued that the main problem was safeguarding the welfare of those going to Syria "who may be driven because of the huge concern over there - some for humanitarian purposes - naively to go out there".
But there was also "a real worry about those who may be radicalized, who may have been engaged in terrorist training", he added.
Militants with suspected links to al-Qaeda have been heading to war-torn Syria from many other countries since war broke out in 2011.
Reports say at least 500 British militants are operating in Syria.
The war in Syria started in March 2011, when pro-reform protests turned into a massive insurgency following intervention of western and regional states.
The unrest, which took in terrorist groups from across Europe, the Middle East and North Africa, has transpired as one of the bloodiest conflicts in recent history.
SHI/SHI