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,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 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."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,. Most have been placed in rehabilitation schemes instead.Earlier this year the Telegraph revealed that the Home Office is paying a leading mental health clinic to treat returning jihadists and their children.And in 2017, the Government's terrorism laws watchdog, Max Hill QC, suggested returning jihadis should be reintegrated rather than automatically prosecuted because they were simply "naive".Overall, the report found that thirteen people were killed and 46 injured in attacks by jihadis across Europe in 2018. The figures were the lowest by far since 2014, when Isil swept into control of a third of Iraq and Syria and launched a campaign of mass casualty attacks in Europe."Europol's report underlines that terrorism still poses a real and present danger to the EU," Europe's Security Commissioner Julien King said in a statement."The enduring threat posed by Islamist groups along with the rise of far right-wing extremist violence, clearly shows that there is still much to be done - notably in tackling the scourge of terrorist content online."