So can any info for the year model be derived from the four digit number? I can find no S/N info online at all.
I often feel I'm speaking in an empty room...my final comment -
1. Geoffrey Butler did not
build frames, they bought them in from the trade: this means (put crudely) that they put their decals on another builder's frame.
2. We do not know that this frame was supplied by GB, it may simply have GB decals on it.
3. Frame serial numbers are very tricky in this context for obvious reasons (we do not know the builder - many trade frames did not have the same identifying number as the builder's own frames).
4. GB sourced framesets from a particular group of suppliers/builders and Roberts were not
one of them.
I knew GB very well, and despite that they did not build frames they were a well regarded shop, and notwithstanding the fact that I walked/cycled past the shop twice a day for 6/7 years they were a part of my cycling landscape for longer...another Croydon shop was my LBS though. Roberts cycles was never a shop in the same sense as GBC.
Tell your American cycling buddies it's a Roberts - they'll never know, after all it is the nation that put Mercedes Benz grilles on VW Bugs (I lived there for 18 months so qualified to comment) !
I could mention it also produced the biggest fraudster in the history of cycling but that would be churlish!
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, 2 x very early Roberts (late 60s/early 70s), 1975 Bill Philbrook tourer, 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.