Research by academics at the University of Warwick found that those with a private school background earned 2.5 per cent more than their counterparts - even if they were the same sex, had studied the same subject and gained the same class of degree.
The study, using the job destinations of 50,000 graduates leaving the "old" universities in 1993, found that earnings also varied considerably depending on which university a graduate attended. Graduates from Oxford and Cambridge could expect to earn 8 per cent more than the average. Other universities scoring highly included the London School of Economics, Imperial College, Exeter and Bristol.
The report said: "It appears that the old school tie does matter, even when all else is equal."
The research follows a study published earlier this week showing former state school pupils got better degrees than their independently educated counterparts. Independent school pupils were one-fifth less likely to graduate with a first.
The Warwick study also found large variations in the pay of graduates from different courses. Those who studied law or politics were paid 27 per cent more than humanities graduates. Computing graduates also commanded high pay rates, but language or science degrees produced a relatively poor return.
The class of degree also has a major influence on pay, researchers found. First-class graduates could expect to earn 6 per cent more than average, while those with an upper second were paid 2.5 per cent more than the norm. Holders of third-class degrees, however, were penalised, earning 5 per cent less than average.
Dr Naylor said: "When Tony Blair says, 'Education, education, education', it's really education, family background and school background. Graduates who went to independent schools are likely to get better paying jobs. It's the old school tie network - effectively discrimination - and we found that seems to be what is happening at the point where you go into a job. It is also possible that independent schools equip people better for certain jobs."
The study also has important implications for the debate over university "top-up" fees. Academics in elite institutions argue that students gain more from their courses and so should pay more than the standard pounds 1,000- a-year tuition fee.
But Dr Naylor said such a move would simply discriminate further against students from low-income backgrounds.
Carl Gilleard, the chief executive of the Association of Graduate Recruiters, said: "It may be that independent schools make you more assertive and confident to compete for jobs, but clearly in some areas it's still important who you know.
"There are all sorts of subtle factors which influence how firms choose recruits. Soft skills like communications and confidence are important. If you go to an institution with an outstanding reputation it does rub off and it may give you a better chance when you go for a job."
t Sir Clive Thompson, captain of industry and bitter opponent of the pounds 3.60 national minimum wage, is paid nearly 130 times as much, it was calculated yesterday.
As Sir Clive and other senior figures in the Confederation of British Industry (CBI) gathered for their annual conference, they were accused of "rank hypocrisy" for attacking the statutory floor on pay.
The union-funded Labour Research Department estimated that Sir Clive, CBI president, is paid pounds 466.34 an hour - more than double the minimum hourly wage every minute. Sir Clive, chief executive of Rentokil Initial, has recently defended his company for paying the lowest average wages among companies in the FTSE 100 index.
He predicts that the minimum wage, due to come into force on 1 April next year, will cost his company around pounds 5m a year. The CBI called for a minimum of pounds 3.10 to pounds 3.20 an hour.Reuse content