Super weird sculpted fillets or welds or something and a long seat tube. Guess you can kind of date it to the early 90's with that Mavic 317 headset, which are sweet because the top nut tightens with an allen key instead of another 32mm nut. But the rest of the parts are pretty hodge-podge so who knows.
EDIT. Mercian Cycles says its filleted and was built around 1984. via CLEfix