By day they were ordinary civilians — from dentists and clergymen to gamekeepers and roadmenders – in a Britain gripped by fear of imminent invasion by Hitler’s blitzkreig troops.

The only clue to their alter egos might have been the pieces of paper in their pockets – informing any police officer suspicious of their behaviour “to ask no questions of the bearer but phone this number”.

But new details have now emerged of the highly secretive role played by a “resistance” army of fit young men and women chosen as would-be saboteurs and spies in the event of a German landing.

In the dark days of 1940, the unit grew to about 6,000 members, who knew little of each other and operated in small guerrilla groups. Recruited to disrupt a German occupation force – including roles such as blowing up tanks, lorry parks and communications – the teams prepared by carrying out covert missions, known as “scallywagging”, at night.

The Auxiliers, as they were known, formed operational patrols of seven or eight heavily armed men who emerged from hideouts to watch the coastlines of East Anglia for any sign of approaching German commandos.

Their role was to engage in irregular warfare, which meant that, as civilians, their capture by the Germans would have led to their instant execution as spies. Not everyone in the military hierarchy approved of the concept, believing that only men in uniform should be recruited to fight the enemy.

Official records of the GHQ Auxiliary Units – whose creation was authorised by the inner War Cabinet, chaired by Winston Churchill – have rarely been released by the National Archives.

Now John Warwicker, a 78-year-old retired Scotland Yard Special Branch officer, has unlocked some of the secrets and written an account of the resistance organisation-in-waiting, called Churchill’s Underground Army. “There is unnecessary secrecy about these units [but] Britain’s stay-behind army of civilian men and women should not be cast aside or written off as insignificant,” Mr Warwicker said.

Even those recruited for bombing missions never knew who was really behind the idea. Mr Warwicker said that they had thought they were working for the War Office, but GHQ Auxiliary Units were financed by MI6, and one element of it, the Special Duties Section, became so experienced in covert operations that after the threat of invasion receded, members of the section were snatched up by the SAS for the rest of the war. Some of the Special Duties Section spies were women.

Many of those who were recruited into the Auxiliary Units had been selected from the ranks of the Home Guard – yet as one senior officer recorded at the time: “To compare them with the Home Guard was to compare the Brigade of Guards with the Salvation Army.”

“They were a secret guerrilla group – the members were not to know each other. As cover for their activities they were to appear to continue their lives entirely normally,” Mr Warwicker said. The key man in each patrol group had a store of explosives and weaponry hidden away and only he knew where it was.

When the idea was first mooted in 1940, recruiters were dispatched around the country to find suitable candidates: men and women who had not been sent to war because they were needed on the land or in other vital jobs. The trawl included clergymen, gamekeepers, poachers, dentists and roadmenders. “A minor police record was not necessarily a disadvantage,” Mr Warwicker said.

Each operational patrol was also issued with one gallon of rum. The jar was to be opened only to relieve pain in the event of injury or in the face of imminent capture, in the belief that “a tot or two might help to extend the time an auxilier could be expected to resist interrogation and torture”. In 1944 an ungrateful War Office demanded the return of every jar of rum, unopened and still with an official seal. It failed to notice that many, while still apparently sealed, were filled with green tea – or something similar.

‘I said I would do anything’

Case study

Don Handscombe, an early recruit to Churchill’s underground army, recalls the moment when he was arrested by a sharp-eyed police constable who wanted to know why he was scurrying around at night with a revolver in a holster.

Now 90 and living in Suffolk, Mr Handscombe told The Times: “I said I was with the Home Guard but he didn’t believe me. He didn’t like the look of me — this was after Dunkirk when we expected to be invaded. I had to spend a few hours in a police cell until our intelligence officer arrived to release me.” After that, Auxiliers were given a note to produce in such circumstances.

Mr Handscombe, who was trained in explosives and marksmanship, had been recruited while he was working as a farm manager: “I was asked what I was prepared to do for my country and I said I would do anything.”

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