Ah Well!
These generic Nervex-lugged frames are very difficult to identify, and while your frame has what might be the initials of frame-builder stamped on the bracket, it is nevertheless a difficult call.
It's a pity that you have not taken a head-on photo to show the head lugs, but from what I can make out the lugs appear to be Mk 1 Nervex Pro - those with the two little spikes sticking up as opposed to the later model with the twirls.
The Chater Lea ends - clearly the gear hanger is not original - coupled with the spear-point seat stay top-eyes and, of course the Nervex lugs set the frame in the very early 50s or maybe even a few years earlier..
I am not too sure that the fork is original - with its Wagner crown it looks very similar to the ones used by Holdsworth on many models.
I have just remembered that I have a frame in my collection with all these same features except for the fork crown...and it is an early Hill Special built by Adam Hill in Padiham, Lancashire.
Hill Specials were very renowned in the 40s and 50s and were in fact sold throughout the UK by agents.
The Classicrendezvous archive and photo site has a feature on Hill Special frames as well as a lead to Robin Hatherall's Hill Special site.
Examining the frames and bikes on these two sites similarities, with Ken's frame can be seen., particularly the spear-point top-eyes as shown on the white frame of the CR site and other features such as the mudguard eyes fixed part way up the seat stays and fork blades instead of on the drop-outs.. Hill also scolloped out the rear end of the Chater Lea rear drop-outs. This is a treatment that I have not seen on other Chater Lea drop-outs..so I do not think, but obviously could be mistaken..that it is a regular C-L model of drop-out.
The low number. 218 on the fork column, assuming that the fork might just be original, would put the frame in and among Hill's frames made in 1950...just about the correct age for this frame.
Two other points might just clinch the origins of the frame. Hill Specials used a special rear brakes bridge treatment whereby each end of the bridge was filed to produce two little prongs that wrapped around the seat-satys for rigidity. Also it is likely that the head tube would have had a metal badge with two holes in the vertical plane.
If your frame has any of these features then it is probably a Hill Special, although it has to be rememberd that many features such as top-eyes, mudguard eys etc were common to many brands such as Maclean, some Bates etc etc. Robin would be keen to help out as far as possible.
Hope this helps
Norris Lockley..Settle Uk