Ok - Fork now removed. The steerer tube has the same number, 5142 stamped into it so it is obviously a matched set.
So what I have here is:
One lugged steel frame, campagnolo dropouts for-aft. Badged with MB (of Dronfield) on seattube and headtube. 120 mm OLD. I think it is 531, I have no badges. But the weight lends itself.
Anecdotally it was built up once, and this is the build. Vernon states the number isn't one of theirs. The area it comes from is Derbyshire though. I suspect it was, at least, finished by them. The interior tubes look fantastic. I can't see it being built up more than once. The paint job looks to be the original too.
Cranks are 1973 Strada, Brakes are 1975 Weinmann 500, hubs are shimano dated 1978 which would indicate the bike was built circa 1979. Tis possible the parts were all bought from what was in stock. They are all in good condition, patina aside. Hardly any use to nothing to indicate any parts were used beforehand. The only thing which is a little odd is the use of Sugino Mighty chainrings on the crank.
Milremo seatpost, fujita Saddle and 3t stem and Cinelli bars are all of the same late 70s period, along with the 980 rear mech and Record 3 hole front mech.
Any information anyone may be able to shed would be gratefully received......