When I worked in a Lancashire factory in the early '60s (student vac job), many of the old-timers brought the makings of their tea in their snap tin. The bottom part of the canister was the teapot - with tea leaves and condensed milk in the bottom part - and the smaller top part was the cup. All fitting snugly and carried by a wire handle. At break time, the canteen hot water - scalding hot, by the way - was used to fill the tin, and there was the tea for an hour or two.

A habit from army days, I gathered.