Research by Kingston University in southwest London suggests that there has been a 50% rise in numbers over the past six years.

In a survey that asked 130 students whether they knew any friends involved in the sex industry, one in 10 said they knew of students who had stripped, lapdanced or worked at massage parlours and escort agencies to support themselves. Just over 6% said they knew students who worked as prostitutes.

The academics found that alcohol and mental problems led some women into stripping and lapdancing. But those resorting to prostitution were simply working to earn money.

University tuition fees, first introduced in 1998 at £1,000 a year, have risen to £3,000 this year at all but a few universities. The average student loan at graduation last year was £8,948, but NatWest Bank said that once private debt was factored in, students now in their first year could expect to graduate with liabilities of more than £14,700.

Dr Ron Roberts, a health psychologist who was the lead author of the study, said: “Our figures represent a 50% increase in the prevalence rates for student prostitution since 2000 . . . given the increasing financial problems experienced by students, this is in line with what we would predict.”

The researchers talked to students in different age and social groups and cross-checked descriptions to avoid double-counting sex workers who might be known by more than one respondent.

Roberts and his co-authors, Sandra Bergstrom and David La Rooy, called on education and welfare authorities to acknowledge the problem of increased costs forcing students into sex work.

According to a 2004 study, clients spend an estimated £534m a year on prostitutes — almost as much as Britons spend on going to the movies. The average cost per encounter was £55, more in London.

Last week one London escort said she had been working in the industry since 1999 to support herself through a masters degree and now a doctorate in international politics.

“In the agency lounge, we all had our books or our laptops,” said the escort, who would be identified only as Sophie. “We were all studying at night, then would take breaks to go out with the guys.”

Sophie said she could sometimes earn £2,000 for a full night’s work in 1999, but now competition from eastern European prostitutes had driven earnings down, while tuition fees had gone up.

“Instead of working in McDonald’s, or shops for £8 an hour,” Sophie said, “sometimes it is easier to work in this industry, make more money quickly, pay the rent and have time to do your reading.”

Internet adverts for escort agencies and massage parlours boast of having “college girls” on their books. Sophie said: “If clients are willing to pay up to £350 an hour, it’s because they don’t want a bimbo. They want a conversation as well as sex.”

Sam Heuston, 24, a contestant last year on Big Brother, said she earned £80 a night stripping and bar-dancing at clubs when she was studying marketing at Oxford Brookes University.

But Gemma Tumelty, president of the National Union of Students, warned that students in the sex industry were vulnerable to abuse.

A spokesman for Universities UK emphasised that the institutions provided support services for students in trouble, but “students are responsible adults and we treat them as such”. Though tuition fees were £3,000 this year, students could wait to pay them until they graduated and were earning.

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