Thanks, that's fair enough as far as it goes.
This means that it was a development of the [1930s] Continental frame, initiated by Raleigh who at this time, were "Carlton".
From the early 1950's as far as I've seen on many photographs, all Carlton frames had brazed-on cable stops on the righthand side of the top tube for the rear brake cable.
The frame that I have bought has only Campagnolo cable clips on the top tube and I'm pretty certain that someone would not either remove the braze-ons, or persuade Carlton / Raleigh to leave them off.
There still appears to be no rational explanation for the curved rear stays - and I haven't seen any photographic evidence or otherwise, to suggest that this curved frame style was available for sale from a retail outlet, or even illustrated / specified in a Carlton catalogue.
I'm still researching and will report any new findings.
Thanks to all for your comments and opinions which I find fascinating and very interesting.