BBC Education Correspondent Mike Baker reports

Martin Jenkins and Jenny Dolphin quit their posts at Halton College in Widnes, Cheshire, with immediate effect.

They left, citing ill health, within 24 hours of the publication of a National Audit Office report which found the college was unable to justify spending more than £6m of public money.

The report said overseas trips taken by college staff were "out of all proportion to any of the benefits the college claims to have derived from them".

Over a five year period, Mr Jenkins and Mrs Dolphin spent nearly 12 months away from the college at public expense - including several "jet lag recovery days". They attended most of the overseas trips together at a cost of £210,000.

The report also questioned the use of "away days" and the level of personal expenses claimed by college staff.

"This college does not have adequate controls in place to ensure that away days are justified in advance, or that they offer value for money," wrote the report author, Professor David Melville, Chief Executive of the Further Education Funding Council for England.

"The college has not satisfied me that public funds have not been used to pay for an unacceptable level of personal expenses, such as bar bills."

Halton College was also found to have incorrectly claimed money for ineligible students from the funding council.

And it claimed funding for more than 60 hours "guided learning" for 1,200 students on an "introduction to further education" course, when the course only lasted three to four hours.

Baroness Blackstone: "What has taken place at Halton is simply not acceptable"

The principal and deputy principal were suspended last year following allegations from a member of the public about their conduct and use of public money.

A statement issued by the college on Thursday afternoon said: "Mr Martin Jenkins and Mrs Jenny Dolphin have resigned from their positions as principal and deputy principal of the college. Their resignations take effect immediately.

"Mr Jenkins and Mrs Dolphin were the subject of a disciplinary investigation. The college presented its evidence alleging gross misconduct by both Mr Jenkins and Mrs Dolphin. At this point, Mr Jenkins and Mrs Dolphin resigned, citing ill-health."

A survey of more than 100 further education colleges, carried out by the National Audit Office and published with the report, concludes that some of them may have similar weaknesses in financial controls.

The report censures the Halton College's governing body for failing to adequately monitor the management of the college, particularly the activities of the principal and deputy principal.

Its conclusions include the recommendation that college governors should be given a financial report at least once a term, so that any problems can be addressed quickly.

'Not acceptable'

Halton College has been ordered to repay about £400,000 to the funding council immediately, and may eventually have to return up to £9m.

The Education Minister, Baroness Blackstone, said: "What has taken place at Halton is simply not acceptable.

"I have no hesitation in issuing a clear warning to other colleges that any repetition of this sort of behaviour will be dealt with quickly and severely."

Before its financial difficulties, Halton College was seen as a pioneer of the expanding further education sector. At one time, the college had 40,000 students and a turnover of £22m a year.