I believe there is a number on the seat tube which corresponds to the month and year of manufacture. It usually is "alanmyy" so it would appear your bike corresponds to a 1980. This makes sense with the conventional dropouts, as way back, I had a 1979 with the same dropouts and now have an 83 with vertical dropouts. Good luck with your resto.
Thanks chap. A definite answer. 1980! I was but a lad of 9 years. All I need for this build are a couple of suitable tyres and I will try and get it in the next road BoTM.
Today's mood... Middling, middling to poor.