Probably from the 1950s, definitely a custom build. A James Lenton of Cardiff (i know nothing about them?) 50cm c-t seat tube, 56cm c-c top tube. Fillet brazed, very neatly. Nervex fork crown. Cable and shifter braze ons. The cable stops are very neatly slotted. brazed on sturmey pulley wheel. Original paint. Blue or faded to green, with red box lining. Frame number 232, so either a very early one, or not many were made! Period headset / bb and seat pin fitted. $130 plus shipping. Airmail to the us would be $85.
Regards
Martin Coopland