National Dried Milk, Ministry of Food, Tin - these were given out actually during the 1940s and continuing for some years

This example shows:  'Ministry of Food' and the white background which seems to be consistent with a 1940's/WWII tin

This is a very informative link:  http://www.cooksinfo.com/national-dried-milk

This tin is 7.5 inches tall x 4.5 inches diameter

The stamp on the bottom will possibly give someone 'in the know' an idea of its source/age - I think it says:

SJ1/25

Not many of these available now..