It never fails to spark a debate in the pub - but now people applying for civil service jobs are being asked it too.
Government bosses want to know how working class their staff think they are - when compared with most people.
The answers will not be used to decide who gets a job - but to help recruit a more diverse workforce.
The question will be: "Compared to people in general, would you describe yourself as coming from a lower socio-economic background?"
The options are: Yes, No, Don't Know and Prefer Not To Say.
Applicants will also be asked whether they were entitled to free school meals, the type of school they went to and their parents' occupations and qualifications.
The government has drawn up the questionnaire with leading employers, including telecom giant Telefonica O2 and accountants Ernst and Young.
Some employers said they did not want to ask staff and job applicants to rate their own socio-economic background because it would be too subjective, according to the consultation document.
But the civil service said that particular question had proved popular with its staff and managers - so they would continue to ask it.
James Turner, chief executive of social mobility charity The Sutton Trust, said asking about socio-economic background "in isolation" would have limited value.
"Anecdotally, when you ask working class people about their social status, they inflate it. There is a tendency to try and sound posher than they are.
"The opposite is true for people from affluent homes."
But he argued that taken together with the other questions on family background and schooling, it could help make the civil service more diverse.
A Cabinet Office spokeswoman said: "We are determined to become the UK's most inclusive employer.
"To monitor progress against that aim, we need to build a picture of our workforce, and one part of that is socio-economic background.
"We want the brightest and best working in the Civil Service and our whole approach is to level the playing field and make sure opportunities are open to everyone, regardless of their background."
The initiative was also backed by the civil service union The First Division Association.