To follow up on what Muley Gil said:
Right after the loss of so much of their equipment at Dunkirk, the Brits were desperate for anything that would shoot. There are written accounts of their civil defense forces having to guard airfields armed with swords, pikes, and battle axes!
All across the US, barrels for civilians to donate working firearms were placed in sporting goods stores, hardware stores, etc. Apparently, they would take anything. I remember seeing a letter in one of the gun rags circa 1990 from an Englishman who wrote about a lever action Winchester in his possession that had come over to England in those dark days. The US government was busy sending whatever they could to England as part of the lend-lease program, so it may have come from military stores or from a civilian.
About this particular revolver:
The "45.900 7 tons" is the British description of the 45 ACP cartridge:
bullet diameter = .45 inch,
case length = .900 inch,
pressure = 7 tons (14,000 pounds) per square inch.
It was not converted from .455 Webley.
Is the finish still blue? Many of these were Parkerized at US arsenals.
Are the stocks (grips) original? (IE, do they look like the ones in the picture above?) If they are original and in excellent condition, they add a lot to the value of the deal.
That price is not too far out of line for one in good working order. Without seeing it, it's hard to say whether it was refinished or not, or whether it's a good deal or not.
