"Jihadi John” is pseudonyms given to a member of the ISIS terrorist group alleged to be a British national and is known for his role of apparently beheading several prisoners in 2014.

An intelligence expert has told how evidence has been discovered showing a dozen or more suspects have provided the ISIS executioner with “money, contacts, and facilitated travel to Syria”.

The revelation comes after agents compiled one the “most extensive dossiers” on those behind the British killer whose identity is known by MI5 and the FBI.

Our source revealed all of his friends and contacts in Britain had been identified and that a web had been uncovered “stretching from Dewsbury to London”.

An intelligence expert commented: “Those supporting this terrorist face a simple choice – either co-operate with inquiries or face the full force of the justice system. There is nowhere to hide.”

Counter-terror police officers acting on US intelligence have found and tracked suspected members of his terror support network in the UK.

The Sunday Mirror understands up to a dozen suspects have already been targeted by the authorities.

Last month the FBI confirmed they knew “Jihadi John’s” true identity but details have deliberately not been made public while intelligence officers continue to monitor the movements and electronic ­communication of his alleged helpers.

Some of the suspects were already known to British security services and have been linked to previous UK-based terror plots.

It is also understood that friends of Birmingham-born Junaid Hussain, one of Jihadi John’s close associates in a gang of British IS fighters dubbed “The Beatles”, have been co-operating with intelligence officers.

A US intelligence source close to the investigation said: “The emphasis has been to track down the support network around the British IS executioner because we know they are still communicating with him.

“There has been success in this approach and our monitoring techniques have exposed British members of a tight network that is actively sending funds and resources to IS fighters in Iraq and Syria.

Former London rapper Abdel – Majed Abdel Bary, 23 – shares several physical attributes with the killer and had been considered a suspect.But voice recognition experts believe it is not him.

There has also been confusion over whether the man seen talking in the beheading videos is the same person who carried out the executions.

Using only the man’s eyes — the only part of his face left uncovered in the video – they have pieced together a photofit style picture of what they say lies underneath the mask.

The US source said: “High-tech imaging techniques have been used, but it is still only a very good guess at what the killer could look like.”

Other experts are using the IS beheading videos to determine exactly where and when the Western hostages were beheaded.

US experts now say it is possible that two militants appear in the video. Both dressed in the same black garb, they could be switching places between frames.

In the James Foley video, the man speaking has a pistol holster underneath his left arm — a sign that he is right-handed. But the masked fighter who beheaded Foley did so with his left hand.

In another sign of inconsistency, the knife the man held at the start of the video does not appear to be the same knife shown next to Foley’s decapitated body.

Two weeks ago “Jihadi John”, believed to have beheaded two British and two American hostages, was reported to have been injured in a US-led air strike.

The masked ‘executioner’ with a London accent is believed to have narrowly escaped death when he attended a summit of the group’s leaders in an Iraqi town close to the Syrian border last Saturday.

“Jihadi John” is reported to have been rushed to hospital after the air strike in Al Qaim, in Anbar Province, Western Iraq.

The Foreign Office said: “We don’t have any representation inside Syria, so it is difficult to confirm these reports.”

The joint US-Iraqi mission left at least 10 IS commanders dead and around 40 injured.

“Jihadi John” has become one of the world’s most hunted terrorists after the beheading of British aid workers David Haines, and Alan Henning, as well as American journalists James Foley , Steven Sotloff,  Peter Kassig, and an unknown Syrian soldier.

Unlike most other western recruits, Jihadi John has risen to a ­position of some seniority. Normally, Western fighters occupy lowly positions.

He is believed to have been a prison guard for IS and has risen to be a member of a shura council, or governing body, of an IS ‘wilayat’, or province.

“Jihadi John” is aged between 28 and 31, and is fluent in English, Arabic and classical Arabic, the language of the Koran.He first joined IS in Iraq when he left the UK, but then moved to Syria.

He is said to travel around in a black Audi jeep, and has six other British terrorists with him who act as his bodyguards.