It's usually the C2s who are credited with having swung strongly to Thatcher from the Labour Party: the C1s would always have been more skewed towards the Tories anyway. Politicians like Norman Tebbit were very much associated with the Tories' popularity among C2s, and they were almost certainly the biggest group which took advantage of the right to buy their council houses during the 1980s.
It's an entirely nonideal scheme for carving up the population, but it keeps being used because it's the one market researchers developed in the 1950s, and it's closely related to purchasing power, so there's a lot more data on who these people are and what they think than for any alternative schema.
Basically:
A: Upper middle class (professional, higher managerial), 3% of households in 1991 census B: Middle class, 16% C1: Lower middle class (junior managers, routine white-collar non-manual), 26% C2: Skilled working class, 26% D: Semiskilled and unskilled working class, 17% E: Residual Category (those on dependent on state benefits, mostly), 13%
[Summary of data in Adonis & Pollard, A Class Act, p.8]
Academics tend to use the "Goldthorpe" I-VII schema of higher salariat, lower salariat, routine clerical, petty bourgeoisie, foremen/technicians, skilled manual and unskilled manual, which they think is more helpful for studying voting behaviour and some other things.
My hunch is that people talk less about ABC1s, etc., in political discussions under the Labour Government than they used to under the Tories, but that may be my imagination, and if so, that may be because there's no obvious swing group to determine the results of elections: Tory support fell dramatically across all social classes.
C. --
========== Chris Brooke Magdalen College Oxford OX1 4AU
http://users.ox.ac.uk/~magd1368/