The Timewatch programme was shown again on BBC 4 last week. Very interesting - I had it on the HD but erased it after watching, otherwise I'd send you a DVD.
Cobham achieved an amazing level of publicity for GA in the 20's and 30's - he says in interview that aeroplanes will "soon be as common as cars are today" which turned out to be a little over-optimistic, and worked tirelessly to promote aviation, and, it has to be said, his own career.
Interesting fact - when WW2 RAF entrants were asked about previous flying experience, 75% had their first flight with Cobham!