It is certainly not a pre 1950 bike. Due to the mounting of the bottlecage which only took place around somerwhere in the 70's withouth clamps, as well as the eyelets on the toprube for cabling, second half of the 70's. To my opinion a bike around at 1977....
Braze-ons for bottle cage bosses were available from some UK builders as early as 1964, indeeed my 1964 Allin Belgique
has them and I have the contemporary price list verifying this.
This is NOT a comment related to the OPs machine.
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 ealry 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.