During WWII there are a number of photographs of showing WInston Churchill in a general officer uniform for the British Army and the RAF. As Minister of Defense did he give himself a promotion to Major General?

No, they were honorary appointments: Churchill was an Honorary Air Commodore of No. 615 Squadron in the Royal Auxiliary Air Force, and was also Colonel-in-Chief of two hussar regiments in the British Army, the 4th Queen's Own Hussars (his old regiment) and also the Queen's Own Oxfordshire Hussars.