The majority of part-time students were women

The number studying a first degree part-time rose from 103,545 to 188,360.

The Higher Education Statistics Agency later cautioned that most of the rise was due to a change in the way the Open University recorded its students.

Part-timers comprised almost a quarter of all undergraduates and 41.7% of all students in higher education.

The majority - 370,480 - were "other undergraduates" - doing sub-degree courses such as foundation degrees, HNDs and HNCs.

The statistics agency added a rider to its figures, saying that about 80,000 Open University students previously coded as "other undergraduates" were now coded as doing first degrees.

But the growth in the number of part-time undergraduates is already causing concern about the potential impact of the proposed higher tuition fees in England and Northern Ireland.

Last week an open letter signed by more than 20 vice-chancellors said part-time students must be given fair treatment over tuition fees.

Labour's proposed variable fees of up to �3,000 a year from 2006 allow full-time students to defer repayment until after they graduate.

But part-time students would still pay their fees, which are typically pro-rata, in advance.

The Conservatives and the Liberal Democrats have said they would scrap university tuition fees - but this does not apply to part-timers.

'Cash-strapped'

At its meeting in February, the board of the Higher Education Funding Council for England (Hefce) said it was "particularly concerned that financially disadvantaged students may be deterred from studying part-time following the introduction of the new fee and student support regime".

Responding to the latest statistics, the vice-chancellors' organisation, Universities UK, said the next government must provide the funds to meet the full cost to institutions of teaching part-time students, and to provide those students with better financial support.

"Unless the government takes action, the provision of part-time higher education will become less attractive to cash-strapped universities, just when we ought to be making the most of the strengths of this form of higher education."

It noted that part-time students made up more than half the student body in 11 universities.

Research carried out last year by the Open University on behalf of the Department for Education and Skills found that the average part-time student was aged 37, female and in full-time paid employment.

Fees varied a lot but for eight out of 10 of the 2,338 responding to the survey they were between �400 and �1,000 a year.

Support from employers varied but about half had all their fees paid for them.

Extra costs for such things as books, equipment, travel and childcare tended to be paid by the student - and often represented "a great burden", averaging �257 a year.