1947 Hobbs of Barbican Clubweight Build and many other old builds

From Classic Lightweights

A. Wheel diameter.
It is my observation that of the frames that we find nowadays MOST of those built before 1950 are built for 26 x 1 ¼” wheels and MOST after were built for 27 x 1 ¼” wheels. I know that 27” wheels were introduced pre-war and am surprised regularly by finding frames built in the very late 1950’s that take 26” wheels. Whichever size they were built for there was invariably clearance for mudguards too. Very few frames were built without mudguard clearances and they would mostly have been pure track frames. These rare items can be identified by having no drillings for any brakes. An observation is that many of the frames built for 26” wheels are now being ridden with 27” wheels (or “sprints” or modern smaller wheels in them), these show a reduced mudguard clearance.

and from the Brown Bros 1952 Catalogue p253 as to what was available a few years later