There doesn't appear to have been an official policy in RAF Bomber Command regarding sidearms for crew. R. C. Rivaz writes in his autobiography Tail Gunner about filling his pockets before a mission:

"... revolver... torch... pipe... tobacco pouch full... thermos flasks of hot coffee... extra scarf and gloves... money... clasp-knife... matches... these are the essentials I always carry."

Similarly in Martin Bowman's Nuremberg: The Blackest Night in RAF History, Wireless Operator Ronald Hammersley mentions that:

"We were then issued with a flask of tea or coffee, with chocolate, sandwiches and an apple; armed with a 0.38 revolver and parachute."

In contrast George "Johnny" Johnson writes in The Last British Dambuster

"I've even heard of someone who was offered a revolver when he was being issued with his kit but refused it because he didn't have anywhere to put it. That's a different RAF from the one that I was in. I was never offered a personal weapon and, as far as I know, neither were any of the others on our crew. If you were forced to bail out over enemy territory, with heavily armed German troops hunting you down, a service revolver wouldn't really have been much good for self-defence anyway. Seems like poppycock to me."

Fear of lynching was certainly a valid concern, though. In Muted Applause? British Prisoners-of-War as Observers and Victims of the Allied Bombing Campaign over Germany (part of Bombing, States and Peoples in Western Europe 1940-1945), R. N. Wylie writes about Lynchjustiz; incidents occurred from mid-1943, but increased in 1944 with official promotion of vengeance for "acts of terror" such as low level attacks on civilians and shooting German fliers in parachutes. Wylie says that estimates of fatalities from lynching range from 350 to 1,500; Richard Overy in The Bombing War: Europe, 1939 - 1945, puts the figure at 225 to 350 and notes that this is a small fraction of total air force prisoners of war.