Sorry for the huge delay in replying to those kind enough to answer my question. Thanks! I was too used to dealing with metric bikes! the MK III has been restored and is now in regular use on the Totnes bike path down in Devon. My Mum took an instant shine to it. Someone far more knowledgeable than me has pointed out several anomalies between other Mk IIIs and this bike:
Colour: Appears original and is a deep burnt orange with a black rear triangle.
Rear Hub: Sturmey 3 speed dated 11/1968 but no drum brake.
Rear Brake: Matches the front. Both are chrome callipers.
Pump Pegs: On the main down tube.
Kick Stand: The remains of this are on the rear triangle and not the BB.
There is a frame number which is 26969. I would love to post a picture but can’t find an attachment method?
Thanks in advance for any ideas!
Mark