Four British police officers are under surveillance after being identified as possible Al Qaeda spies, it is being reported.

MI5 — Britain's equivalent to the CIA — discovered that the so-called "sleepers" — or agents under deep cover — were planted to keep Al Qaeda abreast of anti-terror raids planned by London's Metropolitan Police, According to the U.K.'s Daily Mail newspaper.

Investigators are said to be closing in on the agents — believed to be of Asian descent and living in London — only in recent weeks. The suspects are said to have links to Islamic extremists in Britain and Al Qaeda training camps in Pakistan and Afghanistan, the Mail reported.

The police officers — still on active duty — were identified during an investigation into police force infiltration which has been going on since the July 2005 London bombings, the Mail reported.

MI5 agents are watching the four suspects — who work at different police stations around London — and gathering evidence needed to make arrests.

Click here to read the full report in the U.K.'s Daily Mail.