The UK's top firms are “systematically excluding” clever applicants because they come from working class backgrounds a new government report has found.

As many as 70 per cent of job offers from the country's most elite law, accountancy and financial services firms were made to graduates who attended selective state or fee paying schools, which make up just four and seven per cent of the UK's population.

Interviews with the firms, which employ a combined 45,000 people, found that much of this was caused by recruitment attempting to take a more “cost-effective and efficient” approach.

One employer admitted it “boils down almost to a budgetary” issue. “Is there a diamond in the rough out there… how much mud do I have to sift through in that population to find that diamond?”

Another agreed saying: “We’re trying to be relatively efficient in our process, so, would we, kind of, dig and dig and dig and dig?”

Another explained that having previously hired someone who was working class they lacked certain “polish”.

They said: “We need to talk about the way that she articulates, the way that she, first, chooses words and, second, the way she pronounces them… I’ve got a lot of clients and a lot of colleagues who are very focused on the personal presentation and appearance side of it.”

Alan Milburn, the chair of the Social Mobility and Child Poverty Commission, said: “This research shows that young people with working-class backgrounds are being systematically locked out of top jobs.

“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.”

He added: “They are denying themselves talent, stymying young people’s social mobility and fuelling the social divide that bedevils Britain. It is time for the rest to follow the lead of the best and adopt policies that make access to a top job genuinely meritocratic.”

Dr Louise Ashley of Royal Holloway, and research project lead, made three key recommendations – to amend attraction strategies to encourage a higher number of applications from students from more diverse backgrounds; to ensure they have access to similar levels of support as colleagues from “more traditional” backgrounds and “interrogate current definitions of talent”, including how potential is identified.

Adopting these three strategies would “ensure that disadvantaged students are not ruled out for reasons of background rather than aptitude and skill”, she said.