Universities and colleges are more than twice as likely to employ staff on controversial zero-hours contracts as other workplaces, freedom of information requests have found.

More than half of the 145 UK universities and nearly two-thirds of the 275 further education colleges that responded to the requests said they used the contracts, which do not specify working hours and often give limited guarantees on conditions. The FoI requests were made by the University and College Union (UCU).

Among businesses in the wider economy, according to recent research from the Recruitment and Employment Confederation, just over a quarter (27%) of companies use zero-hours contracts.

The UCU president, Simon Renton, said: "Our findings shine a light on the murky world of casualisation in further and higher education. The widespread use of zero-hours contracts is the unacceptable underbelly of our colleges and universities."

Just under half of the universities that responded to the union said they employed more than 200 staff on the highly flexible work contracts that do not guarantee any work or pay, can restrict employment elsewhere and can also deny holiday and sick pay. Five institutions including Edinburgh, Bath and Kingston universities employed more than 1,000 people in this way.

Universities contacted by the Guardian said that many different kinds of teaching-related staff could be put on zero-hours contracts including visiting lecturers, PhD students who also taught, examiners, teaching assistants and specialists who might be brought in to help out with specific research projects.

UCU said use of the contracts was "haphazard" and it was difficult to gauge their exact use within institutions. Some universities, for example, might put all their PhD students on zero-hours contracts in case they chose to engage in teaching, but those students might never actually work for the university.

According to the information it provided to the UCU, Edinburgh University appears to have 2,317 teaching staff on zero-hours terms – the highest number in the survey. A spokesman for the university said "significant numbers" of staff were on the flexible contracts but no more than 5% of work carried out in the university was paid for in this way. He added that some staff on zero-hours contracts were freelancers who were free to work elsewhere.

In a statement, the university said it had started to phase out the contracts: "We are committed to ceasing the use of 'hours to be notified' contracts and to offering all employees guaranteed hours. We have already started this process and anticipate that the majority of employees presently on 'hours to be notified' contracts will have guaranteed hours by the end of this calendar year."

Bath University, the second most prolific in using zero-hours contracts according to UCU's data, said only staff working less than the equivalent of one day a week were on the flexible deals. It said those working on the contracts accounted for less than 5% of the total hours worked by its academic staff.

However, it told the UCU that it had about 200 teaching staff on zero-hours contracts in June who had worked during the last 12 months. That total is nearly two-thirds of the total number of teaching staff listed on its books by the Higher Education Statistics Authority.

The UCU said some universities were using the flexible contracts to help keep costs down during a tough period for the academic sector and "flexibility" could mean workers were unable to make financial or employment plans for the year or even the month ahead.

Philip Roddis, a 60-year-old part-time lecturer in computing and related

subjects, attempted to take Sheffield Hallam University to an employment

tribunal for unfair dismissal after his hours were suddenly reduced from an

average 400 a year to about 50.

Roddis said he was unaware that he was on a zero-hours contract with the

university until embarking on the legal action, which was thrown out at a

pre-hearing. "It was all in the small print," he said. "It's been pretty devastating, I'm living on savings and am lucky that my kids have grown up and my mortgage is paid and I've got a bit of income from elsewhere. I don't suspect there was malice but people like me aren't very visible and I feel the university doesn't really care."

Research released at the start of August suggested there could be around 1 million workers in the UK on zero-hours contracts. That estimate, produced by the Chartered Institute of Personnel and Development, suggested zero-hours deals are far more commonplace than official data indicates. The Office for National Statistics increased its estimate to 250,000 just days before the CIPD released its research.

The Guardian has identified nearly 200,000 workers on zero-hours contracts across the private sector, including staff at McDonald's, Burger King, JD Wetherspoon, Sports Direct, Cineworld and Boots. The government has also admitted that 307,000 workers in the care system are on zero-hours contracts, which leave staff unable to guarantee their income each week, making it difficult to get mortgages or loans

The topic is to be debated at the TUC conference this weekend. The business secretary, Vince Cable, is undertaking a review of zero-hours contracts for the government but the probe has already been branded inadequate by Labour.

• This article was amended on Thursday 5 September 2013 to make clear that Philip Roddis' case was rejected at an Employment Tribunal pre-hearing.