Great looking bike Scozim. (You could stay at my place for a while.

)
Looks a lot like the 1976 Mercian Olympic frame I bought a few years ago. Immaculate paint and lug lining.
55cm CTT
Wrap over seat stays
Mine has a TDG Italia headset
The bike Scozim posted about has a Mercian badged Tange headset. Looks more like hardened grease and dirt rather than rust. Nothing a wire brush won't clean up.
Top locknut from another bike.
verktyg