Nick, nice find in a way as I have been looking for a good example of a Model 37 for some time; just as a curiosity, as I don't think many were imported to the U.K.

This is what I have on the subject. The .410 model was introduced in 1940. If is lacks the depressed 'W' mark on the underside it is post 1948. They stopped making them in 1963.

Odd why they are scarce over here at the side of Harrington & Richardson's which turn up often. Lagopus.....