Hi,
While I am not all that well versed in the history of men's London hatters, this does have an early 1950's look to it. How wide is the brim in front, how tall is the crown in front, and is the brim edged with ribbon? Is the inner logo/seal covered in plastic? These give clues.....also the thinner ribbon hatband went out of style in the later 1950's, so that may help date it also.
It is a really stylish hat. It is not a trilby, it looks to be a snap brim fedora with a teardrop crown.