Not all of the manufacturers of the WD jerry cans were based in the UK, and even those there were 'based' in the UK may have had manufacturing plants outside of the UK. The company you are looking for may have been making these cans in any British Territory such as Canada, India, New Zealand, Australia, Aden etc.
Particularly in war time it is fun to see where some British companies had operations. Rio Tinto for instance was a London based mining company that operated Zinc mines in Spain.