Thanks for the photo - very interesting, dutchman! It looks like an air raid shelter - maybe as a refuge from a gas attack. Incidentally, I remember thta most casualties in Coventry were those who took refuge in the Market Hall cellars.
It's noteworthy that the Germans had far more air raid casualties than need have been because they didn't build many air raid shelters for the public (unlike for Party officials!) Part of the reason was the much more common practice of having cellars and underground garages. In Dresden, a lot of people were killed due to toxic gases and fumes, where they had taken refuge in the cellars of the baroque houses; the cellars were connected house to house, so when fumes entered one end, they couldn't be escaped, and often the fumes entered the other end, too. Many house interiors collapsed onto the cellars, closing access to them, with the result that people who may have survived the fumes and the fires died of asphyxiation. The cavern under Owen Owen would have given protection from mustard gas, though, and that was what our authorities expected. The snag is, the Germans had SARIN and TABUN; the only reason Hitler didn't authorise their use was that he was convinced that we had them too, and would retailate with them! If SARIN had been used, we would have suffered millions of civilian deaths.
Re the HG weapons: one of my uncles was in the HG, and they were all taught to use a Sten. I remember him telling the story of them being in a line up on the range, all told to fire a short burst, and one guy had his Sten keep firing; of course, he was daft enough to turn round as the magazine emptied, accompanied by dozens of people hitting the dirt in a flash!! (I bet he was on a charge!!!

) HG rifles were largely obsolete, too. Old (WWI) pattern Lee-Enfields and Ross-Enfields; they were effective, so long as you didn't expect to hit anything! My brother in his National Service had to use a Ross-Enfield; he said that his score was 39% - and that's with static targets on a range. (A comparison: when I was a pistol shooter, I achieved about 92%, with a Browning - not a wonderfully accurate pistol) I think it was probably wise that the HG didn't have modern weapons - they might have killed someone (but probably not the enemy!!

); they would have probably helped keep heads down for a bit, to buy time for the army to arrive.
Your Bevin Boy got off lightly! In Stalin's Russia, being 20 minutes late for work resulted in a 12 month jail sentence.