Early war until about 1942 or so the British Army used a white enamel mug with cobalt blue on the lip. This was then replaced by the brown mug more commonly found. Both are correct for later on in the war, but for North Africa and Italy, the white one is proper.
Late war mugs were often (olive)green, mostly you find this colour on the lower version, (always?) dated 1945. Last year I discovered a mug (in my opinion a real British) in a shop at St. Mere Eglise. The shopkeeper used it as a pencilholder. Because it was behind glass I couldn't examinate it. It was not for sale, too bad! . Last month I discovered a high model in the same green colour in Belgium. It had no markings on its bottom, but becaused it was priced just one euro, I couldn't resist leaving it there.
A surplus shop in my area that I visited earlier this week has lots of the white ones (genuine surplus)..and they have them in two sizes....I didn't check the dates though it's most unlikely they are wartime dated. I know the Navy had them for a long time after the war..'Nice cup of Cocoa, Sir?'...Ian
I bought a few on e-Bay , the modern Falcon enamel mugs. Once you peel off the Falcon sticker there are no markings on the mug. Just a white enamel mug with blue rim, I got the 9cm mugs but there are 8cm ones available too.
http://www.ebay.com/itm/New-Falcon-White-Enamel-Mug-Beaker-Cup-Tea-Camping-9cm-/370501598001?pt=UK_HomeGarden_Kitchen_Cookware_GL&hash=item56439dbb31
Once you've sorted out the authentic mug, you've got to get the awful WW2 tea exactly right too! Spike Milligan described it as thick, brown and lukewarm.
Due to cross contamination of petrol and water cans in the First World War, Capt. Rawlins of the ASC said that the tea had far more petrol in it than actual tea and the petrol would probably have been perfectly safe to drink as it was about 9 parts water to one part petrol!
A surplus shop in my area that I visited earlier this week has lots of the white ones (genuine surplus)..and they have them in two sizes....I didn't check the dates though it's most unlikely they are wartime dated. I know the Navy had them for a long time after the war..'Nice cup of Cocoa, Sir?'...Ian
Go back and buy the lot we can all have one instead of a cap for the d day 200 for 70 bike run