Hmmm, my orange 1980 carlton appears to be the same bike, and has a 531 Main Tubes DB decal, and forged Suntour dropouts. And my orange 1980 carlton criterium weights only 80 grams more (6.77 lbs) than a 1975 Raleigh Team 531-throughout frameset from Ilkeston, in the same size...
Here is a 1981 Carlton Criterium :
http://www.carltoncycles.me.uk/
So I think you are a little to dismiss all Carlton Criterium bikes as "gaspipes"...
- Don Gillies
San Diego, CA