The Further Education Funding Council report, published last week, says that around 28 per cent of full-time equivalent teachers are on part-time contracts.
Lessons taught by part-time staff are generally of poorer quality than those of full-time lecturers, said the report, which calls for better training and support for part-time teachers.
And though some colleges are seeking to give part-timers more job security, many others find staff through outside agencies.
During 1998-9, the two largest FE teacher agencies supplied some 25,000 part-time teachers to around 200 colleges and both are predicting their business will rise during the current year.
Tower Hamlets College, east London, has begun a three-year programme to switch hourly-paid part-timers to fractional contracts that give them similar rights to permanent staff.
Principal Annette Zera said that the use of hourly-paid staff was undermining efforts to raise levels of literacy and numeracy in the area.
The majority of part-timers teach either basic skills or creative arts subjects.
It will cost the Tower Hamlets college - which employs about 300 part-timers - about pound;100,000 to put them onto contracts that reflect the numbers ofhours each of them teaches.
Most were pleased to be offered permanent contracts, said Ms Zera, although she added that a minority wanted to remain on hourly contracts and had turned down opportunities for staff development.
"There is a question over whether we will be able to carry on employing these people in the long term," she said.
"We want staff who will be our people all year round rather than just rushing around from one venue to the next."
Liverpool Community College tries to persuade all basic skills lecturers to teach at least 12 hours per week rather than spending too much of their working time in other colleges.
However, only a third of its 46 part-time basic skills teachers are on contracts.
The remainder are employed through agencies and therefore paid on an hourly basis.
Janet Gathercole, basic skills development manager at Liverpool, said the minimum 12 hours these part-timers would spend in the college each week meant that they had more opportunity for important pastoral work with students.
"It's important we make sure they are committed to working in the college," she said.
Barry Lovejoy, national official for FE at the lecturers' union
NATFHE, applauded those colleges that are rejecting casualisation.
"We are optimistic that there is going to be a move towards a high-quality employment model for part-time staff," he said.