Seat tube has been cut down and a pinch bolt brazed on in place of the original clip ?
Does the head tube have bi-laminate lugs with something filed off.......
Hence my comment creatively modified
, viz the seat tube and head tube. Regarding the head tube; strange, but not a bi-laminate CB. I've only seen a grease nipple on a head tube on pre-war or very early post war frames (not on a Hobbs or CB though).
The orange frame (I've seen previously) has Hobbs distinctive/trademark alloy seat tube clip missing (Hobbs used a very different one from CB) - I can provide images if desired.
The crimped chainstays may offer a clue. Also Hobbs of Barbican stopped building frames in 1953, this is well documented.
N.B pre war Hobbs frames did not have a letter prefix to the frame number.
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.