A fictional operator featured is the Dreadnought Motor Traction Co, of Wantage, run by Captain Ricketts (played by Terry-Thomas). His yard has a double deck open top bus (1920-1930 era) being used as an office showing registration number LA 9928, apparently an ex LGOC B-type; this is the registration of preserved B340:
Seen in the yard are two derelict early Bedfords, apparently WTBs, one
front-entrance, one rear-entrance. I couldn't see registrations on either, although I have CCR's report of JT8077, a Duple-bodied Bedford WTB now preserved.
Lead of the two coaches that arrive to take the schoolgirls to
Rome is Bedford WTB UD9381. This has 'Thame' as its destination. It's
towing Bedford DL9779, which is abandoned en route.
In Rome itself this Fiat coach is glimpsed:
"The classic line from the film being -
Q -'Will we get to Rome in these?'
A - 'Well we have come all the way from Wantage.' " (thanks Vic Gackowski)