That frame looks so similar to mine. Mine is badged as a "Jaguar", but doesn't have 531 stickered forks. Aside from that its the same colour, same head badge, braze on cable guides on the top tube, 531 sticker in the same place by the levers rather than on the seat tube.

I think yours would have come with 700c "clincher" wheels, and 5 or 6 speed Suntour gears originally. It looks great - I've not seen an Atlantis except in blue before.

Year? My 1980 (or so) Dawes had stops and housing to run the gear cable under the bottom bracket, but the replacement frame I got in the mid-80s had a plastic guide under the BB to route bare wire.

Tony S