I thought hat it would be prudent to try to heal the north v south divide in the UK by agreeing with Mike that the mystery frame on UK Ebay certainly has all the hallmarks of a Claud Butler "Avant Coureur"
As far as can be seen from the pictures it is a fully lugged model and not a bi-laminated example which had no "lug" down the seat-tube. Judging by the Chater Lea rear drop-outs it is probably no later than the late 40s very early 50s. I could be wrong though because I have a Claud B track frame complete with cast lugs cut to a very similar but not identical design, D-section forks though which dates from an earlier period.
Over to Hilary?
Norris Lockley.. with an after thought..
Why use a seat-lug and not have a seat-bolt eye.. and why use the Italian collar type clamping?