some bloke diddled me brolly in the queue for the khazi in
blighty

The phrase "diddled me brolly" doesn't sound authentic to me. You would either say "diddled me out of me brolly" (i.e. conned or swindled me out of it), or use a more appropriate slang verb such as "nicked", "pinched", or even "'alf-inched" (rhyming slang for "pinched").

It sounds like the sort of dialogue an American would write for a supposed Brit (reminds me of that bloody awful character in Frasier, Daphne's brother, an American playing someone supposedly from Manchester but spoke with a sort of pseudo-cockney accent) ;-)

Mind you, I don't want to start a US v Brits feud here - I'm sure there must be equally bad examples of British "American" scripts :-)