Terrorism-related arrests of far-right extremists have also risen to their highest since records beganCredit:Joel Goodman/LNP The figure was the highest since records began in 2001 and three quarters of the arrests were for international terrorism, almost all linked to Islamist extremism.But the number of right-wing extremists arrested also rose to a record high after a neo-Nazi group called National Action in December became the first extreme Right-wing group to be banned as a terrorist organisation.The surge in far-right extremism led to a jump in the number of white people being arrested, up from 68 to 113.The Home Office released the latest figures as police and MI5 have said they are dealing with an unprecedented threat from Islamist terrorists planning attacks in the UK.The statistics were released as the European Union’s own law enforcement agency warned about the threat from home-grown “stay-at-home” jihadists. Fewer jihadists are heading to Iraq or Syria as Isil’s self-style caliphate shrinks in the face of an international air campaign backing Iraqi, Kurdish and Syrian rebel forces.As the caliphate has dwindled, jihadist propaganda has encouraged would-be terrorists to remain at home and carry out attacks on civilians. A Europol report warned: “Ongoing contact on social media between combatants in Syria/Iraq and ‘stay-at-home jihadists’ fuels the enduring potential threat posed by jihadist networks; now that leaving the country to take part in jihad has become more difficult, would-be attackers may indeed shift their focus to their countries of residence.”The Home Office figures include 12 arrests made as part of the investigation into the Westminster attack in March. All were released without charge and told they would face no further action.Since then, there have been two more deadly attacks, in Manchester and London Bridge, while counter-terror agencies have foiled five alleged plots.After the Manchester attack police and MI5 said they were dealing with an unprecedented threat and were running 500 investigations involving 3,000 individuals at any one time.There are also 20,000 former “subjects of interest” whose risk must be kept under review.A National Police Chiefs’ Council spokesman said: “The UK’s counter-terrorism network is currently dealing with an unprecedented level of demand. Stops made at ports and airports under counter terrorism powers fell sharply as the number of people heading to join Islamic State in Iraq and Levant (Isil) dropped, the Home Office said. A4amVqYjE6kqCejZUPd3mlD0kxfy_H9R “Police forces across the country are working closely with partners to bring an increasing number of suspects before the courts under terrorism legislation, and where they cannot do that they are using criminal legislation to disrupt terrorist activity.”Officers and staff are working tirelessly to overcome this growing threat, but they need the public’s help to do so effectively.” Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings. Police arrested a record number of terrorist suspects last year, as fewer would-be Islamic State group jihadists head to the Middle East and instead decide to stay at home to plot attacks.The number of arrests for terrorism-related offences in Great Britain jumped by nearly a fifth, with 304 people held in the year until the end of March.