This story revealed how MI5 is using a fleet of surveillance aircraft to search for Britons fighting alongside the Taliban.

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In the same edition of the newspaper we also had another exclusive story this time about how it was feared a UK air base had been used by the CIA as a stop off point for one of its controversial terrorist rendition flights.

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Spy-in-sky patrols over British cities in hunt for Taliban fighters

Mail on Sunday newspaper

MI5  is using a fleet of sophisticated surveillance aircraft to search for unidentified Britons who fought alongside the Taliban in Afghanistan.

The manhunt has been ordered because it is feared the committed and highly trained fighters may have returned home to plot terror attacks in the UK.

Planes with eavesdropping equipment are now flying over British cities searching for returning Afghan fighters.

They are attempting to identify suspects using 'voice prints' of fighters with British accents picked up by RAF Nimrod spy planes monitoring Taliban battlefield radio signals.

The revelation comes after the former SAS commander in Afghanistan yesterday confirmed that British Muslim extremists were actively supporting Taliban and Al Qaeda attacks on British troops.

He said there was also evidence that these people were then returning home to plot further attacks in the UK.

Brigadier Ed Butler warned: 'There is a link between Kandahar and urban conurbations in the UK. This is something the military understands but the British public does not.'

Whitehall sources have never officially confirmed that the three Britten-Norman Islander aircraft based at RAF Northolt in West London are being used for covert surveillance by MI5.

One of the Islander aircraft

One of the Islander aircraft

Last year it was revealed that West Midlands Police had used the aircraft, which can monitor computer and mobile-phone communication and long-wave radios, to track suspects connected to the plot to kidnap and behead a British Muslim soldier.

And their long-term role with the Security Service was apparently confirmed by a photograph, obtained by The Mail on Sunday, of an MI5 surveillance officer, Steven Lanham, who died on duty in 1999, dressed in a flying suit alongside one of the aircraft.

The Islander aircraft regularly patrol the skies over Birmingham and Coventry, Leicester, West Yorkshire and the bordering Greater Manchester areas, flying at between 12,000ft and 15,000ft.

Their equipment and capabilities have never been officially disclosed but they are believed to be able to monitor mobile-phone calls. More recently they have been fitted with equipment capable of picking up signals from wi-fi computer networks.

'Traffic' intercepted by the equipment on board is analysed and processed, probably at the GCHQ spy centre in Cheltenham, searching for voice matches with those overheard in the Afghan war zone.

Voices heard in Afghanistan and the suspect voices in the UK are computer-analysed looking for a match. It is understood that, in some cases, it has been possible to determine the true identities of the Taliban fighters from the UK.

Last night Whitehall sources refused to discuss MI5 surveillance methods.

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