Three men have been arrested on suspicion of terror-related offences after police raids in Hertfordshire and Bedfordshire, just north of London.

Police said then men were arrested at a business address in Letchworth and two residential addresses in Luton. Two are believed to be in their 20s and the other in his 30s.

Witnesses report that one man screamed “cowards” at police as he was dragged away from his workplace at Alliance Healthcare in Letchworth. An eyewitness said: “I was outside and an unmarked van came screeching round the corner quite fast and then the police were dragging him from inside.

“I heard him shouting his head off calling the police cowards. The man was lashing out as he was being taken away. He was quite a big lad, quite muscular.”

The men are being held on suspicion of “being involved in the commission, preparation or instigation of acts of terrorism”.

A spokesman for Scotland Yard said: “Today’s arrests and searches are part of an ongoing investigation into Islamist-related terrorism.

“They were also assisted in the execution of one of the arrests by officers from the Met’s Specialist Firearms’ Command. No shots were fired.

“Searches are under way at two addresses in the Luton area as part of the investigation.”

Sources told the Daily Express that the men are suspected to be part of a “fairly advanced” Islamist conspiracy to commit an atrocity in Britain. Investigators are looking into possible links between the group and an Al Qaeda cell in Pakistan.

Last week, Breitbart London reported that counter-terror chiefs met to discuss raising the UK’s terror threat level to “critical”, meaning an attack is imminent. The meeting followed the terror attack in Tunisia that claimed the lives of 30 British holidaymakers.

A security source said that “the threat of terrorism now is probably at it’s highest for eight years,” adding that Britain faces “a really serious threat from Islamic State.”