A couple of days ago I watched the episode Cheering Up Ludovic, in which there is a reference to Foggy's Burma campaign. Compo and Clegg joke about Foggy retaking Burma. Clegg asks was that the first or second time, to which Compo says, either time it wasn't so clever because "thee had help". Foggy then replies that the biggest help they had was that Compo wasn't there. He says "and probably the biggest help we had out there was that you never left England". To which Compo replies, "I were guarding Gloria Quarnby".
Point is there are quite a few references to Foggy being overseas in Burma and I don't recall any saying that he wasn't there, but as a Corporal Signwriter he may well have been out there as support. I think his fantasy was that he was in the thick of the action, when the chances are he was well behind the lines and never saw any but heard lots of stories.
Interesting though that later we have the story of Compo at Dunkirk, but it's clear from the early series that there are numerous references to the fact that he never left England.