Not that hard to define really;
"The working class is the class of people employed for wages, especially in manual or industrial work. Working-class jobs include blue-collar jobs, but also include large amounts of white-collar and service work."
So basically anyone that is employed ? That covers around 90% of the workers in this country !
Just out of interest how many of these professions would you class as working class :
Bank Manager
IT Consultant
Deputy Head in a School
Vet
Army Officer
Farmer