Up to eight police officers and civilian staff are suspected of links to extremist groups including Al Qaeda.

Some are even believed to have attended terror training camps in Pakistan or Afghanistan.

Their names feature on a secret list of alleged radicals said to be working in the Metropolitan and other forces.

The dossier was drawn up with the help of MI5 amid fears that individuals linked to Islamic extremism are taking advantage of police attempts to increase the proportion of ethnic staff.

Astonishingly, many of the alleged jihadists have not been sacked because - it is claimed - police do not have the "legal power" to dismiss them.

We can also reveal that one suspected jihadist officer working in the South East has been allowed to keep his job despite being caught circulating Internet images of beheadings and roadside bombings in Iraq.

He is said to have argued that he was trying to "enhance" debate about the war.

Classified intelligence reports raising concerns about police staff's background cannot be used to justify their dismissal, sources said.

Instead, the staff who are under suspicion are unofficially barred from working in sensitive posts and are closely monitored. Political correctness is blamed for the decision not to sack them.

It is widely feared that "long-term" Al Qaeda sleepers are trying to infiltrate other public sector organisations in the UK.

In November last year, it was revealed that a leading member of an extremist Islamic group was working as a senior official at the Home Office.

MI5 has warned in the past that suspects with "strong links" to Osama Bin Laden's killers have tried to join the British security services and, in January, exiled radical Omar Bakri claimed that Islamic extremists were infiltrating the police and other public sector organisations.

Suspicions are growing that the gang behind the failed London bomb attacks could have received inside information about rescue procedures in the aftermath of an atrocity in the capital.

The Daily Mail can reveal that the second device parked near Haymarket was left at a designated "evacuation assembly point" where civilians and the emergency services would have gathered had the first bomb gone off.

Investigators are trying to establish whether the bombers knew the significance of the location.

Sources said it is unlikely that the Met is the only force which may have been infiltrated by Al Qaeda sympathisers.