Bravo.
After searching probably thousands of googled photo's you finally found one with a .50 HMG on a Firefly.
The Browning .50 was standard equipment on most US vehicles and also used by the ground troops. If you google normal M4 Shermans, M8's, Stuart light tanks, M2/M3 halftracks, US supply trucks, boats, ships...etc you'll see almost every one has a .50 on it.
Not so with the British vehicles.
They didn't use the .50 HMG as standard equipment. If you google Churchill tanks, Matildas, Comets, Cromwells, British armored cars, trucks, boats, ships, etc. you will not see a .50 cal in sight.
It is obvious through your diligent searching that there were a few .50's used by the British. Again, it was not common.