A few of my thoughts as I knew many of the South London/Surrey builders BitD, I'll wager the wrapover seatstay appeared first on Holdsworth frames, then widely copied.
Alec Bird, Ken Bird's Brother built many of the Clive Stuart team frames, and the seat stay arrangement (e.g the integral allen bolt clamp) is a signature of many of the Bird frames, as are the drilled lugs.
The earliest frames I've seen featuring drilled lugs are Roberts (Chas Roberts senior), and apart from featuring on Bird frames they also appear on early Ron Coopers (both my Ken Bird -Alec Bird built - and my Ron Cooper have drilled lugs), my Ken Bird has the fastback stay too.
Ken Bird is in the Herne Hill photo. Ken passed away a number of years ago and Alec is still around (I do see him occasionally at jumbles). I have quite a large catalogue of Bird frames; and the larger percentage were built by Alec (this too was the case with Clive Stuart frames).
Could add more but I'm worried about your attention span!
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.