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.
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.
Omar Altimimi, a failed asylum seeker jailed for nine years yesterday for hoarding manuals on how to carry out car bombings, had applied to work as a cleaner for the Greater Manchester force.
In a separate development, it is understood that a policeman was removed from his post after concerns about his conduct in the aftermath of a major anti-terrorist operation in the past two years.
For legal reasons, the Mail cannot reveal any more about the case.
The MI5 list of suspected Islamists working in the police is said to have been drawn up in the aftermath of the 7/7 terror attacks in London.
MI5 checked staff details at the Met and other forces with intelligence databases on individuals said to have attended radical Islamic schools - or Madrassas - and terror training camps in Pakistan and Afghanistan.
It is thought that intelligence files on those who frequently visit pro-Jihad websites and who have associated with so-called preachers of hate were also compared to details of officers and civilian staff in the Met.
As a result of the review, eight officers and civilian staff were identified as Al Qaeda sympathisers or people of concern because of their links to Islamic extremists.
The disclosure will raise concerns about the system for vetting new recruits, each of whom is the subject of counter-terrorism checks to ensure they are suitable to join the police. Scotland Yard's vetting unit is regarded as one of the best in the country.
But sources said it is often impossible to carry out satisfactory checks on recruits who were raised overseas or who have spent considerable periods out of Britain before applying to join the Met.
In such cases, the Met has to rely on overseas agencies to carry out intelligence checks on their behalf. Privately, officials doubt whether certain countries in Africa, Middle East or the Indian sub-continent are able to carry out meaningful vetting.
As a result of the Stephen Lawrence public inquiry report, which accused the Met of being "institutionally racist", Scotland Yard has in recent years employed thousands of officers and civilian staff from the ethnic minorities in an attempt to reach recruitment targets.
A Scotland Yard spokesman said: "All employees upon joining the Met and during their careers undergo a range of security checks. These are robust and vary according to the type and sensitivity of individual postings.
"We take matters of security very seriously and if an issue arises, people may be subjected to further assessment.
"This may lead to restrictions in relation to where an individual works in the organisation or whether they are suitable to remain in the service."Source: Daily Mail (English)
See also: UK police: you can't fight terror without working with extremist Muslims