"At least back in the day, only wealthy families could afford Sandhurst. He could buy his pistol of his choosing, as did Churchill. Some models would be more available than the other."
By World War II junior officers were no longer required to purchase their own sidearm. They were issued a sidearm.
"As an officer in the tank corps, he could get an inglis hi power from Canada with no fuss, instead of shooting his revolver in a less-than-gentleman manner."
Uhm... No. He couldn't.
Inglis-made Hi Powers weren't available until late 1944. ALL production was contracted to the British government (for British and Commonwealth troops) and the Nationalist Chinese government. One simply couldn't bop over (or drop a letter) and expect to get one.
One the British army started issuing the Hi Powers, they were priority issued to Airborne and Special Forces. No general issue of Hi Powers was made to regular army commands, including armor, until well after the end of World War II.
http://www.ai4fr.com/main/page_militaria__collectibles_canada_inglis.html
"Didn't he shoot out the street lamp with his Luger as a college boy prank (questionable judgement perhaps)?"
Not sure what you point is about this. I've not read the book, so I don't know what the time frame is for when he did this vs when he and his tank landed in France.
"It is still unthinkable the British army didn't teach their lads how to use their weapon properly."
As with most European military organizations, handguns were largely seen as a badge of officer's rank. There are accounts of the British and French being very surprised at how many American enlisted personnel had handguns when American troops arrived in Europe in World War I. Even more surprising to the British was that the Americans viewed handguns as legitimate fighting tools.
The British placed almost no priority on training their officers in the use of handguns. Essentially it boiled down to being shown how to load, unload, and maintain the gun and range time that MIGHT get them up to 50 rounds fired total. If they were lucky. As war time pressures of ramping up an army really hit home, it's very likely that that amount of training was cut considerably. The military needed the officers more than it needed the officers to be proficient in handgun use.
For most of the first half of the war officers were issued a total of 12 rounds of ammunition -- 6 in the gun, and 6 in load loops. Getting more ammunition required it to be requisitioned from regimental stores and likely offering justification as to why you needed to replace your ammunition.
So no. It's not surprising at all that the British didn't properly train their officers how to use the issue revolver.