Most schoolchildren who have Saturday jobs or deliver newspapers in the morning are working illegally, according to a study.

The research found that 85 per cent of under16s with part-time jobs in shops and cafés have no work permit, the document required by law before a child of school age undertakes paid employment.

Businesses face fines of £1,000 if they are caught without a permit for young staff.

Permits are issued free of charge by local authorities so that officials can check that young people are working the correct number of hours and in appropriate jobs. The permit must be signed by the child’s parent and, in some areas, by the youngster’s head teacher.

However, research conducted by the University of Paisley and sponsored by the NSPCC children’s charity, found that hundreds of thousands of businesses are flouting the law, and most local authorities are turning a blind eye. About half of all children aged between 13 and 16 have part-time jobs, a workforce of about 1.5 million, according to the NSPCC. Very few local authorities bother to prosecute businesses for breaking the law on child employment. Surrey County Council is an exception. They hired Ian Hart, a former Metropolitan policeman, to crack down on companies with no permits and other breaches.

In six years he has prosecuted 27 companies including MacDonalds, Tesco, Sainsbury’s, Whitbreads, Woolworths and a number of newsagents and small shops for breaching rules.

“Businesses have admitted to me that it is worth the risk not to bother with the permits because they know the chances of getting caught are so slim,” he said.

In 2004 ministers began consulting on a proposal to replace the permit scheme with a register of all companies who employ children. However, that consultation has been shelved.

Explore Education

• Young Times

• Schools

• GCSE & A Level Results

• Good University Guide

• Sunday Times University Guide

• Student

Times recommends

• Why team games may make your children fat
• Ivy League targets Britain’s top students
• Mini-schools ease transition for Year 7 pupils