Britain had been planning a civilian resistance organisation in case of invasion from as early as 1939. This was, however opposed by the War Office who preferred a military guerrilla force under their control, rather than that of SIS (MI6). Whilst SIS continued to develop a deep cover resistance organisation, in 1940 the War Office created the uniformed Auxiliary Units, based around the Home Guard.
The Auxiliary Units comprised fighting patrols and the complewtely separate intelligence network of the Special Duties Branch.
The fighting patrols of the Auxiliary Units operated from underground hides. Their task was to cause as much disruption to German supply lines as possible - with an anticipated lifespan of no more than two weeks. In 1944 they had an important role in countering expected German commando raids following the D Day landings.
The Special Duties Branch comprised a network of civilian agents and wireless operators. Their short range TRD transceivers, using voice transmission, were all destroyed by SIS in 1945. The example pictued here is a replica (built by Malcolm Atkin with much thanks to Richard Hankins and Project Witney, VMARS). it was not the sujper-undetectable set of legend and in 1944 they also used completely unsecure WS17 sets. In 1944, as part of the deception plans before D Day, the SDB contributed to the production of spurious radio traffic (often reading poetry or knitting patterns) to confuse German intelligence as to the timing and location of the Normandy landings.
[for further information see Fighting Nazi Occupartion by Malcom Atkin, Pen & Sword, 2015.]