Shelf-stacking and burger-flipping into the small hours might pay for mobile phones, brand-label clothes and alcohol, but students under pressure are more likely to underachieve or leave, say college managers.

Colleges have plenty of anecdotal evidence but find it hard to get a clear picture as students under unreasonable pressure from employers do not want their tutors to know. If a college takes up their case, they may be sacked, say colleges seeking a “protocol” with employers to limit workloads.

There is a longstanding tradition of Saturday jobs with a recommended maximum of eight hours a week, often providing useful work experience, but many retailers now expect at least 16 hours a week - “even the ones you think are good”, says Paul Respoli, principal of Reigate sixth-form college. A lack of national guidelines means that tutors must negotiate local solutions.

The Working Times Directive covers all employees, but there is no guidance on youngsters in full-time education. Employers have the right to ask staff over 16 to work up to 48 hours a week, but this will be cut to 40 hours for 16 and 17-year-olds from April.

Big employers such as Sainsbury’s, Tesco and McDonald’s have policies that allow flexible hours around exam times, and say they are aware of students’

needs. “Most students are attracted by our flexible working patterns,” said a spokesperson for McDonald’s. “Anyone can request study leave.”

Tesco says it works closely with schools so that students can work more in summer holidays and less in exam periods. Asda’s policy allows up to 12 weeks a year unpaid study leave and encourages shift swaps.

But college principals have evidence of bosses in retail, catering and call centres who put pressure on students to work unsocial hours or skip classes. They say some employers show no regard for students’ needs.

One call centre expected its employees to attend two weeks’ training during term time or face the sack. One care home employed a student for 30 hours a week on night shifts, and left her to administer medicines.

Students are often under pressure to do extra hours at busy times, or to do unpopular shifts that adult workers do not want.

Dorothy Lownds, principal of Hartlepool sixth-form college, is monitoring students’ paid work and results. “Employers have targets, but so have we.

The Government wants more people to go into higher education but they are dropping out at level 3.”

Miriam Stanton, principal of Bede college in Billingham, said: “Curriculum 2000 began well, but it is difficult to keep students on four AS-levels.

Most see work as a right, and sometimes parents support them.”

A study by the Northern Ireland Economic Research Centre in 2001 estimated that one in six of the province’s students underachieved due to excessive working hours.

Principals in Hartlepool want a protocol after inspectors from the Office for Standards in Education raised concerns about retention and results.

Dorothy Lownds said: “There is a national issue to address. I am working my way round a morass of the needs of students, employers and targets.

“It’s a dog’s breakfast. I’m not sure if the Government realises what’s happening.”

Tees Valley learning and skills council is working with employers to create a protocol. Sandra Morton, the project manager, said: “We hope to liaise with the chamber of commerce and the Small Employers’ Federation. We are taking it seriously.”