The Heathrow worker, now in jail, was one of more than a dozen suspected terrorists allowed to enter Britain, it emerged this weekend. Senior anti-terrorist officers are furious that Al-Qaeda suspects breached immigration checks and that one was able to penetrate the world’s biggest international airport.

The suspect was arrested as he was about to board an international flight. Anti-terrorist officers discovered he was living near the airport and working for an air services company after the Bank of England circulated a list of 17 Al-Qaeda suspects whose assets were to be traced and frozen. Three men were identified as living in Britain. Two were arrested and a third remains at large.

The 17 names were passed to banking authorities by Italian intelligence last October after they arrested several leading Al-Qaeda suspects.

The three men — who had allegedly been in contact with the Italian Al-Qaeda cell — were discovered in Britain in January but the two arrests were not publicised. The pair are being held at Belmarsh high-security prison in southeast London under the Terrorism Act.

One of those detained is alleged to be one of Al-Qaeda’s European leaders. The third man has been convicted in absentia of terrorist offences in Algeria.

He is believed to be a senior figure in Takfir wal-Hijra. The group is now part of Al-Qaeda but is so militant it once tried to assassinate Osama Bin Laden as a dangerous moderate. This third man is believed to be living in London’s Algerian community and has been seen at the Finsbury Park mosque. He was able to claim asylum despite being named on a European Union list of terrorist suspects sent to police and immigration authorities.

Police have made several arrests but are still trying to trace others in the group. The missing men are suspected of being members of two north African terrorist groups: the Algerian Salafist Group for Call and Combat (GSPC), funded by Al-Qaeda, and Takfir wal-Hijra, also known as the North African Front.

Others being tracked by the security services include Ali Khelifi, 33, alleged to be a senior commander in the GSPC. He was allowed to enter Britain last year despite an Algerian warrant for his arrest. Omar Saiki, another alleged GSPC leader, arrived last September. He had been jailed in France for his part in the World Cup bomb plot.

Oliver Letwin, the shadow home secretary, said: “This is extremely disturbing. I’ve been saying for 18 months that the complete administrative chaos in our asylum system offers a secure route to disappearance to anyone with terrorist links.”

A senior immigration officer described the service and asylum system as “a mess”. He said due to fighting in Algeria it was almost impossible to refuse entry to Algerian asylum seekers.

Monitoring those entering Britain was difficult as details had been held on three incompatible computer systems until last month. He said the service was focused on efforts to deport failed asylum seekers.

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