A TES snapshot survey reveals the first evidence of the cap on college budgets imposed by the last government. Some principals have been forced to turn away large numbers of students, or set up lengthy waiting lists.
Others are beginning to contemplate axing expensive minority courses to accommodate demand within their budget ceiling.
This year is the first time numbers in further education have been capped since colleges gained their independence five years ago.
John Brennan, FE development director at the Association of Colleges, said: "A number of sixth- form colleges are facing a position in which demand far exceeds their capacity and are turning away substantial numbers of students."
Dr John Guy, principal of Farnborough Sixth Form College, and an AOC board member, said he was being forced to turn away 150 students, representing nearly 10 per cent of his college's 1,600-strong student body.
The college's take-up rate had also soared, from an expected 88 per cent to this year's 96 per cent.
Dr Guy said: "We are turning students away. I am even now looking at a letter from a parent expressing her deep disappointment."
Peter Newcome, principal of Franklin Sixth Form College in Grimsby, added: "There has been very strong recruitment of A-level students. There are different forces at work in each locality, and here the growth of A-levels has been fairly consistent over the last seven years."
The apparent increase in demand for A-levels shows students still willing to join courses leading to higher education, despite the prospect of bearing full fees and maintenance loans when they enter university in 1999.
Overall figures for A-level enrolments are hard to measure, because unlike GNVQ students, those taking A-levels only register formally for their exams well into the course.
But college leaders will use any evidence of a shortage of places when they press for equality between college and school sixth- form funding, central to their autumn offensive.
The cap on college finances announced in January led to claims that up to 250,000 places would be lost across the FE sector this year. But most colleges said it was too soon to see a pronounced effect.
Many colleges reported full-time enrolments slightly down on this time last year, some citing a "Diana effect" caused by the national mourning coinciding with the peak week for college entry.
Part-time figures were reported to be holding steady, helped by the decision of some colleges to start recruiting early in the summer to avoid the annual rush for places.
There were worries, however, that colleges would slice away courses, possibly in minority subjects, to cope with demand.
Margaret Davey, principal of the City Literary Institute, said she had increased enrolments by 15 per cent by offering 10 per cent fewer courses. "You can end up splitting your own market, trying to do what everyone else does rather than concentrating on what you are good at."
Recruitment to access courses was also reported as strong, despite students facing the possibility of university fees at the end.
Colin Flint, principal of Solihull College, said: "There is very, very strong demand for access courses. Ours were full before we started our official enrolment. Certainly there's very strong demand for this type of education, although I don't think people have really thought yet about the implications of fees.
"Overall, recruitment is looking good. We are always concerned, but we did some very strong recruitment over the summer and although recruitment last week is slightly down on last year we are still ahead of ourselves. It's too soon to be certain, but it certainly looks good at the moment."