Three Muslim extremists plotted to behead British citizens after being inspired by an Islamic State order "to kill civilians everywhere in the West”, a court heard today.

Haseeb Hamayoon, 29, Yousaf Syed, 20, and his cousin Nadir Syed, 22, planned to carry out a terrorist atrocity after a fatwa was issued by IS spokesman Abu-Mohammad al-Adnani, it is said.

The alleged terror cell shared gruesome pictures of beheadings they had downloaded from the internet as well as images of the killers of Drummer Lee Rigby, the Old Bailey heard.

Hamayoon had bought a “Rambo First Blood” knife online and had a picture of a PCSO patrolling the car park of a mosque in Hounslow on his phone, jurors were told.

Prosecutor Max Hill QC said the three men planned between September and November 2014 to carry out a terrorist attack.

"This case involves a plan or a plot to commit attacks against persons in the UK using knives", he said.

He said the inspiration came from the Islamic State fatwa issued in mid-September 2014, warning Americans and Europeans: “You will not feel safe in your bedrooms.”

It ordered followers to “strike their police, security and intelligence members” and said civilians were not exempt from attack.

“Kill disbelievers whether civilian or military for they have the same ruler, both disbeliever, both considered to be waging war.”

Mr Hill said: “This message is saying anyone in a country such as ours is fair game – that’s the central message of this fatwa.

“This is so-called Islamic State taking the fight to countries such as ours.”

He said the three Muslims saw the fatwa on the day it was released, on September 21, 2014, and started discussing it in messages on their phones.

Nadir Syed has already been found guilty of plotting a terrorist attack, while his cousin and Hamayoon deny being involved, the court heard.

“To people of a certain mind, by which I mean Islamic extremists such as these three defendants, the fatwa created a considerable stir”, said Mr Hill.

“As we shall see, these defendants became aware of it on the day of release, and they discussed it themselves at length, in an online chat group under the following key message ‘IS supporters to kill civilians everywhere in the West’.”

He said Hamayoon, who has a Pakistani passport, had bought a “Rambo First Blood II” hunting knife online in early 2014 using his wife's bank account, and the knife was recovered from his home when he was arrested in November that year.

British born Nadir Syed had stored images of Lee Rigby's killers, and the three men had allegedly shared images of beheadings which the prosecutor warned jurors they would have to look at.

“You will not have to look at the full horror of these photos”, he added. “But these defendants clearly found them fascinating and inspiring.”

Nadir Syed, of Ambassador Close, Hounslow, west London, has already been found guilty of preparing an act of terrorism contrary to section five of the Terrorism Act 2006, between September 20 and November 7 last year.

Yousaf Syed, of West Wycombe Road, High Wycombe, Bucks and Hamayoon, of Tudor Road, Hayes, west London, both deny the same offence.

The trial continues.