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The unorthodox tactic, which is seeing SAS units dressed in black and flying ISIS flags, has been likened to the methods used by the Long Range Desert Group against Rommel's forces during the Second World War.

More than 120 members belonging to the elite regiment are currently in the war-torn country on operation Shader, tasked with destroying IS equipment and munitions which insurgents constantly move to avoid Coalition air strikes.

It comes just days after David Cameron gave "carte blanche" for the SAS and SBS to target IS leaders as part of the Government's "broad spectrum" response to the murder of 30 British tourists by ISIS gunman Seifeddine Rezgui in the Tunisian beach resort of Sousse.

Though the Prime Minister is being kept informed, senior military sources last night told the Sunday Express that he would not be required to "green light" every mission.

Instead the teams, part of a force known as the Coalition Joint Special Operations Task Force, are under American command.

Dubbed "smash" the units, which travel in civilian pick-ups, can even launch their own unmanned aerial vehicles, or mini-drones, to scan terrain ahead of them and pinpoint IS forces.

Using a US-developed programme, the UAVs camera system can identify any known High Value Target, digitally transmitting the information as it happens to analysts on the ground.

They are being supported by more than 250 specialists, who provide additional communications support.