Sounds as though he was referring to the underclass rather than working class. Underclass is popularly defined as poor and unemployed. That's too broad for my liking because it would include so many who are employed full time on minimum wage along with perhaps legions of State Pensioners - who are technically unemployed - that claim additional state income via Pension Credit as the law says otherwise they wouldn't have enough money to live on.

I'd say those who are fit and able of working age that survive wholly or substantially on welfare payments make up the true underclass along with those deemed too ill to work because of their lifestyle choices: the morbidly obese, alkies and drug addicts. Add the recidivist petty crims and relatively minuscule number who kip on the streets would account for maybe 5% of the population tops instead of the 20% Johnson suggested.