Re:
Can't see a seam inside the seat tube which has an plastic insert to make a 25.4mm seatpost fit.
There are two numbers on the bottom bracket and the fork tube, 320 & 461. Bob Jackson suggest that these are respray numbers.
The Bob Jackson decals are the right design but the white lettering has a black edge to it, not like the ones the factory used on my genuine 1980 frame, so maybe H Lloyd
I'm thinking 501 as the whole bike weighs 11kg, the same as my 1984 Raleigh Sirocco which is 501.
The components are all dated in the 80's, the oldest being the Huracan saddle which is 1987.
It is a nice ride.