Britain has by far the highest rate of “exceptionally dangerous” returning jihadis in Europe, police chiefs have warned.

A report from Europol revealed that of hundreds of Britons who travelled to Syria and Iraq amid the rise of Isil, nearly half have been able to return safely.

It comes amid widespread concern at the low number of returning fighters and so-called jihadi brides successfully prosecuted in British courts.

According to the annual Europol report, roughly 45% of Britons who travelled to Syria and Iraq have already come back to their home country.

The country with the next highest proportion was Germany, where 33% have returned, while in the Netherlands and Spain the return rate is thought to be just 18%.

The report warned that returning jihadis and their supporters pose a serious ongoing threat to national security.

“Those that have returned garner kudos with like-minded individuals,” it said.

“Their training and experience – such as handling weapons and explosives – makes them exceptionally dangerous.

“Furthermore, EU Member States’ ongoing concern is that these individuals can perpetuate and strengthen their networks both nationally and internationally.”

Out of around 400 jihadists who have returned to the UK, just 40 have been prosecuted. Most have been placed in rehabilitation schemes instead.