Looks a lot like my Youngs (of Lewisham) Marksman, 1960, 531 throughout and Nervex Professional lugs as Ned has mentioned.
There is a mention of Jack on Classic Lightweights, confirms the address and that it was a one roomed shop, but no mention of his frames.
The Stoke Newington location is usually associated with Paris. I've not heard of Baguley: suspect (again Ned might be right) frames were bought in from trade builder.
Nice frameset nonetheless.
Just compared a picture of a Youngs Marksman and they are very similar!
Here's my Marksman for comparison, I've shown the seatstay wrapover and brake bridge as they are different (I don't think yours is a Youngs, but a nice frame as mentioned).
For any Youngs fans out there in RBland
my Marksman has the super rare
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.