Coff,
Just by chance, whilst looking for something else, I came across couple of photographs in Aeroplane Monthly of October 1990 showing ULAS Chipmunks in the 50's ( no strakes
) Taken by John Perrot they depict:
WP845 "C" flown by Tony Winship -Photo a/c flown by Gordon Corps ,later CTP at Airbus.
WB746 "H" en route to Summer Camp at St Eval in 1957.
They have no fuselage letters, having the roundel plus "bar" marking.