I don't know how many Mew Gulls were built, I think they were made not far from here, at the once Gravesend Airport. The father of an old friend of mine who died in November had a hand in designing them, and Jean Battens Percival Vega Gull. Anyway, there is a picture of 3 Mew Gulls parked at Gravesend, one is dark red with gold trim and lettering, one is black, I think the other one is black and white, but not like the one above! Arthur Bage was the designer at Percivals at the time (1930's).
Cheers