A man suspected of plotting a domestic Al Qaeda-inspired terror strike screamed ‘cowards’ at police as he was arrested on his lunch break yesterday.

Eyewitnesses described the suspect being dragged away by masked plain clothes police officers who were waiting for him at the offices of a healthcare giant.

The dramatic scene took place at medical supplies distributor Alliance Healthcare in Letchworth, Hertfordshire, where he is believed to have worked as a driver.

Two other men, aged in their 20s and 30s, were arrested in simultaneous operations at separate homes in Luton, just 13 miles away.

Meanwhile ex-officer worker turned senior ISIS recruiter Abu Rahin Aziz, who was from Luton, was killed in Syria by a drone on July 4, raising fears supporters may launch a revenge attack on British soil.

Drama: A man was yesterday arrested at medical supplies distributor Alliance Healthcare in Letchworth, Hertfordshire (pictured)

Simultaneous: Scotland Yard, including a team of armed officers, arrested three men at the same time yesterday

Security sources said last night that police were forced to act over a ‘fairly advanced’ suspected Islamist conspiracy aimed at an unknown British target.

Link: Ex-officer worker turned ISIS recruiter Abu Rahin Aziz, who was from Luton, was killed in Syria by a drone on July 4

Unusually, the conspiracy was not connected to the bloodshed in Syria or the rampant Islamic State propaganda machine.

Instead investigators are understood to be probing potential links between the men and an Al Qaeda-inspired cell in Pakistan.

Armed officers led the raid at one of the addresses, raising fears police believed the men had access to firearms, although none were found.

An attack by marauding gunmen armed with automatic weapons on a ‘soft’ civilian target is one of the greatest concerns of counter terror chiefs.

The man, aged in his 20s, was arrested at 12.45pm yesterday when dozens of officers confronted him at his workplace, a subsidiary of Boots.

One witness said: ‘There was a lot of shouting happening inside and police were in there arresting him.

‘I was outside and a 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, fairly tall, short dark hair. He had dark skin and was Asian looking.’

The witness said he believed the man worked as a driver for the company but described him as a ‘loner’ with few friends.

‘I didn’t really like the look of him,’ he added. ‘He has a serious face, not very friendly looking. He didn’t have many friends I think he just went there and worked.’

Raid: Two other men were held in Luton, where Scotland Yard carried out simultaneous raids

Another employee said security were informed of the planned arrest and were waiting for the suspect to come back from his lunch break before police swooped.

All three men were being questioned last night on suspicion of preparing acts of terrorism last night as counter terrorism officers searched five properties.

Security sources described the fledging plot as ‘concerning’ and said police were forced to act over fears for public safety.

Earlier this month hundreds of emergency service staff took part in a two-day exercise in which jihadi gunmen ran amok at a Tube station and took hostages.

The raids, a week after the 10th anniversary of the July 7 attacks, highlight the continuing severe terrorist threat.

They came as Scotland Yard redoubled its efforts to stop vulnerable people leaving the country to join jihadists.

Police staged an exercise earlier this month to practice for a Tunisia-style terrorist attack in the centre of London - an attack by marauding gunmen is one of the greatest concerns of counter terror chiefs

Armed police were also seen piling into a disused London Underground station earlier this month as part of the exercise

Counter terrorism chiefs revealed 43 women and girls have been reported missing by their families nationwide over the last 12 months alone.

Deputy Assistant Commissioner Helen Ball, one of the country’s top counter terrorism officers, said young women are ‘highly unlikely’ to ever be able to return.

‘Syria is an extremely dangerous place - the reality of life there is far from the image that terrorist groups actively promote to young women here in the UK,’ she added.

A Met spokesman said the arrests and searches are part of an ‘ongoing investigation’ into ‘Islamist-related terrorism.’

She added: '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'.