Spy planes bristling with the most advanced technology are being used in British skies to hunt down the associates of “Jihadi John”.
The planes carry electronics so sensitive that they can detect heat coming off a keyboard after a button has been pressed.
A team of FBI officers are flying with RAF pilots and collating the intercepted telephone and computer signals before sending them to the USA to be analysed.
More than a dozen US investigators from an FBI Joint Terrorism Task Force flew to the UK, where they are working with MI5 and anti-terrorist officers from the Metropolitan Police Force to identify the man.
An FBI source said: “Electronic footprints might help us pinpoint the location of the British IS executioner because we believe there are associates of his in the UK who are directly communicating with him.
It is believed family members of Jihadi John have been interviewed by Met officers and an FBI agent.
It’s also believed the planes are being used to study the movements of Jihadi John’s suspected Midlands associates.
An intelligence services source said the delicate detection equipment on board the planes had previously been used successfully to work out a suspected terrorist’s computer password because of the heat signature left on the keys.
The intelligence source said the surveillance plane had recently been used over Birmingham in relation to Junaid Hussain – who is suspected of being one of the so-called ‘Beatles’ holding hostages.
The planes are understood to be military aircraft which are sometimes used by the police to find escaped prisoners or stolen vehicles.
“This is not the first time such surveillance techniques have been used in the UK but now the equipment we use is much more advanced.
In 2007 a plot to kidnap and behead a British soldier was disrupted with the help of surveillance aircraft flying over the West Midlands.
It is believed an RAF Britten-Norman Islander plane was used in the hunt for a Birmingham terror cell which was plotting to kidnap a British soldier before beheading him live on the internet.
The Islander is a one or two-seater, low-flying plane with a relatively long range and ability to loiter in the air at low speeds.
The RAF says it uses two of the aircraft in what it calls “photographic mapping and light communications roles”.
The Army says on its website that the plane is usually employed for surveillance. Its other roles include air photography, “support to the “special user” and “liaison flying”.
A Ministry of Defence spokesman last night said he could not comment on counter-terror operations but did not deny that RAF surveillance aircraft were currently being deployed.