Nick Clegg will today call time on the "who you know" culture that prevents many young people from modest backgrounds securing work experience and internships.
The civil service will ban "informal" internships or work experience lasting more than a week from next year to set an example to other employers. Companies will be urged to sign a new "business compact" under which work experience slots would be advertised in local schools.
HM Revenue & Customs will launch a crackdown in professions such as law and journalism where work experience is commonplace, to ensure that people are paid the national minimum wage or receive out of pocket expenses.
Ministers say that many young people miss out because they lack the personal contacts or cannot afford to take an unpaid internship. They believe this is hindering efforts to close the "life chances gap" between the poor and better off.
Mr Clegg will announce his moves when he issues the Government's plans to improve social mobility and tackle child poverty. He will say: "For too long, internships have been the almost exclusive preserve of the sharp-elbowed and the well-connected. Unfair, informal internships can rig the market in favour of those who already have opportunities. We want a fair job market based on merit not networks. It should be about what you know, not who you know."
He will add: "A country that is socially mobile bases opportunity on your ability and drive, not on who your father's friends are."
Mr Clegg's comments are likely to prove controversial with companies and with those young people who do benefit from work experience, who say that it helps them to narrow down their career options and get a foot in the door. Businesses argue that the practice allows them to recruit permanent staff on a meritocratic basis.
The informal nature of work placements means that Whitehall has no official record of how many young people do work experience there. From next year, all civil service internships will be advertised on a central website so that anyone can apply.
Ministers have no immediate plans to legislate to force companies to outlaw informal work experience programmes. They hope that firms will support a voluntary approach by backing the new compact. Their staff will spend more time in schools telling pupils about the world of work and operate a "fair and transparent" selection process for work experience.
The Deputy Prime Minister, who has made social mobility his key policy priority, will admit: "In Britain today, life chances are narrowed for too many by the circumstances of their birth: the home they're born into, the neighbourhood they grow up in or the jobs their parents do."
Mr Clegg will announce that, to measure Britain's progress in tackling the "life chances gap" between poor and better off children, people will be monitored at seven key stages of their life.
These will include recording their birth weight; whether they know the alphabet when they start school; their performance in exams, particularly in English and maths; achievements in further or higher education and their place in the job market when they reach 30.