Can you help to identify these frames, bikes or parts?

seat post size will give you the most information
27.2 = top quality frame, Reynolds 531/Columbus SL
26.8 = mid level i.e columbus Aelle(usually)
26.4 = hmmm Belgian half decent but common and you'll never find the builder, or british middle of the road

below that is low end.

Your frame says to me Belgian (triangles on the top of the fork crown)
check the dropouts do they say Campagnolo or Gipiemme or nothing?
flip it over look at the bottom bracket shell for distinctive cutout shapes
forget serial numbers they never help
threading british or italian on the headset and bb? undo the headset and check under the top nut for this info

Hi Ben

Thanks for the benefit of your knowledge, that's a great starting point for me... I'll check those things out and come back to you, if I may, with as much information as I can find. There aren't any cutouts on the bottom bracket and I can't see any markings on the dropouts, but I'll have the wheels off and have a proper look.

Thanks again,

I'll let you know. Mat