I built the frame up and took it out today for a quick go around the block. Its a very nice ride and good to be on a steel frame again- my regular ride for the last year has been an old aluminium Ribble.
And it turns out it is a J F Wilson frame. I got this nice email from Wilson Cycles: Hi Jonathan, yes that's one of my father's frames, he was the first builder in the UK to shoot the seat stays into a lug low on the seat tube. Jim used to call this style fast back...he also was one of the first to cut off and braze the gear hanger on the rear dropout years before it became commercially recognized. The frame is circa 1979/80. Please look after it, hand built frames always go up in value, esp one built by master builder...unlike the disposable carbonfire rubbish the pros are paid to ride...and which they have to have reinforced with light weight steel for them to do the job.
Wilson's do make nice framesets, a good shop with knowledgeable and ethusiastic staff - not sure I agree with the American's comment though.
The frameset is not that unusual in the treatment of the seatstays and Wilson's weren't the innovators of this style - this subject has been debated for a while in the V-CC and the current consensus is that Tom Board was the innovator.
I have a Cliff Shrubb frame dating from 1967 that has a fastback"cluster", another V-CC member has an earlier frameset (an F.W Evans) that pre dates my frame.
Glad you're enjoying the ride - you should post images of the bike as you've built it.
Co-founder of a V-CC section, member South Eastern Road Club and owner of - 2005 Bianchi Reparto Corse (modern), 1985 Raleigh SBDU Pro Super, 1984 Raleigh LU Corsa, 1980 Allin Stan Butler Special, 1978 Ron Cooper, 1975 Bill Philbrook tourer, 2 x very early Roberts (mid/late 1960s), 1966 Raleigh Superbe Roadster, 1964 Allin Stan Butler Special Belgique, 1951 Hobbs of Barbican S/C, 1950 Hobbs of Barbican S/C, 1947 Hetchins Super Special, 1908 Centaur Featherweight. 1988 Specialized Stumpjumper.