Young people from working-class backgrounds are being systematically excluded from jobs in top legal and accountancy firms, an official report has found.
The chairman of the Social Mobility and Child Poverty Commission, Alan Milburn, accused firms of imposing a "poshness test" effectively excluding recruits whose parents do not have "the right sort of bank balances".
A study of 13 "elite" law, accountancy and financial services firms carried out for the commission found that 70% of job offers last year went to graduates who had been to fee-paying or selective state schools.
The former Labour cabinet minister said the findings should be a "wake up and smell the coffee moment" for employers who needed to ensure their recruitment practices were "genuinely meritocratic".
"This research shows that young people with working-class backgrounds are being systematically locked out of top jobs," he said.
"Elite firms seem to require applicants to pass a 'poshness test' to gain entry. Inevitably that ends up excluding youngsters who have the right sort of grades and abilities but whose parents do not have the right sort of bank balances.
"In some top law firms, trainees are more than five times likely to have attended a fee-paying school than the population as a whole.
"They are denying themselves talent, stymying young people's social mobility and fuelling the social divide that bedevils Britain."
The survey found that, at leading accountancy firms, typically 40% to 50% of applicants had been educated at the elite Russell Group universities and that they received 60% to 70% of all job offers.
"The high proportion of applicants from these universities is a direct result of elite firms' recruitment and attraction strategies, which comprise a variety of campus visits and targeted advertising specifically devised with this aim in mind," the report said.
"The educational and socio-economic background of Russell Group students is not representative of the UK as a whole nor within higher education."
The report urges firms to overhaul their recruitment policies to encourage candidates from a wider range of educational and socio-economic backgrounds, while ensuring they had similar levels of support to those enjoyed by their more privileged peers.
Mark Boleat, policy chairman of the City of London Corporation, the local authority for the financial centre known as the Square Mile, said: "Today's report indicates a huge threat to Britain's social mobility and our economic growth.
"While more employers are creating paid internships and apprenticeships to attract bright young people from disadvantaged backgrounds, too many are still guilty of hiring in their own image.
"Drawing from a narrow pool of private school and Russell Group educated applicants will lead to a skills shortage and generation of wasted talented.
"With the capital alone expected to create an extra 145,000 jobs over the next decade, it is essential that employment opportunities are opened up to the best candidates from all walks of life."