Jihadi John
The masked executioner nicknamed Jahadi John spoke in a British accent when executing hostages in Isis propaganda videos  SITE Intelligence

There has been a six-fold increase in the number of Syria-related terror arrests in the UK, said police, as militants inspired by Isis plot terror strikes in British cities.

Officers arrested 165 people in 2014, for offences including attending terrorists training camps in Syria where militant group Isis control swaths of territory, and the financing, commission, preparation or instigation of terrorist acts, said police.

This compares to 25 arrests for Syria-related terror offences the previous year.

The news comes after foreign secretary Philip Hammond warned this week that the UK is at "very significant risk" from Isis inspired jihadists.

Speaking at a London summit on how to combat the terror threat attended by representatives and leaders from 21 countries, including Iraq's Prime Minister Haider al-Abadi and US Secretary of State John Kerry, Hammond warned against complacency in the fight to "disrupt these plots before they come to the stage of an attack".

Last week, Isis militant Imran Khawaja, 27, of Hounslow, London, who posted a picture of himself on social media holding a severed head, faked his death in an attempt to enter the UK undetected.

Senior national coordinator for counterterrorism policing Helen Ball said: "Last year's arrest figures demonstrate a considerable increase in volume, range and pace of counterterrorism activity in the UK.

"We have been running exceptionally high numbers of investigations, the likes of which we have not seen for many years.

"Several attack plots have been disrupted, of various sophistication, from individuals planning to carry out lone attacks to more complex conspiracies, the majority seemingly directed by or inspired by terrorism overseas.

"The partnership between police and MI5 is very effective, and we are experiencing very strong support from the communities.

"We will continue with this vital work to protect and work with the UK public to combat terrorism in all its forms."

The Home Office estimated that approximately 600 Britons have travelled to Syria and Iraq to fight, with about half having returned.

Tough new legislation designed to bar UK citizens suspected of having fought for Isis returning to the country is currently passing through parliament.