There has been a steep drop in the number of part-time college students in Scotland, according to a new report.

Audit Scotland said more work needs to be done to gauge the demand for college courses.

A focus on funding for the college courses most likely to lead to employment has led to a 14% increase in the number of under-25s on full-time courses since 2007/08.

Over the same period, however, the number of students on part-time courses has fallen by 48%, with women and over-25s most affected.

The auditors said the Scottish Government and Scottish Funding Council (SFC) failed to fully analyse the impact of recent policy changes aimed at boosting younger students on those who cannot get a place.

The report said: "The Scottish Government and the SFC did not assess the impact of all policy changes on student participation before implementation.

"Neither the SFC nor the Scottish Government have analysed how the fall in part-time places and the focus on younger students have affected those who have not been able to get a place at college, and what they chose to do instead.

"There is currently no way to tell if these decreases in student numbers reflect a fall in demand."

Audit Scotland said the Scottish Government and SFC also failed to set out how the benefits of recent reforms including college mergers would be measured and reported.

It highlighted a drop in attainment in 2014-15 from 66% to 64%, as well as a fall in retention rates from 80% to 78%.

These decreases were attributed by colleges to widening access and the major changes experienced over the past few years.

At least 82% of students who left in 2013-14 went on to a positive destination and almost 90% were satisfied with their college experience in 2015.

Auditors said while the overall financial health of the college sector was "relatively stable", financial performance had deteriorated, with four colleges - Edinburgh, Moray, North Highland and Lews Castle - facing challenges.

Caroline Gardner, auditor general for Scotland, said: "While the sector has exceeded its learning targets and maintained relatively sound finances, managing the ongoing impact of reform alongside further change and financial pressures will be a complex and demanding task for colleges.

"The Scottish Government, the SFC and colleges need to work together to improve their understanding of the demand for college courses across the country and create long-term plans for how they will commit finances and staff to meet future need."

John Kemp, SFC interim chief executive, said the body would work with the Scottish Government and colleges to address the findings.

He added: "We will of course take action where that is necessary."

Shona Struthers, chief executive of Colleges Scotland, said the body recognises further work is required in some areas.

She added: "Audit Scotland has recognised that colleges performed well over the last year and that they continue to meet their activity targets set by the Scottish Funding Council (SFC).

"The report highlights the significant changes that the sector has faced, whilst continuing to focus on students and the delivery of high quality courses."

Vonnie Sandlan, president of NUS Scotland, said the findings underline the need for an overhaul of Scotland's student support system.

She said: "It's good to see full-time college places being maintained and increasing, recognising the valuable role full-time education can play in improving youth employment or access to higher education.

"However, that focus on full-time provision does pose a very real risk of excluding those students who deserve a college place but simply aren't able to study full-time."

Opposition parties used the report to attack the SNP's record on college reform.

Scottish Conservative education spokeswoman Liz Smith said: "This report raises a number of serious concerns which have significant implications for the employees of our colleges, for students and, of course, for the taxpayer.

"In particular, it makes clear that the Scottish Government's severe cuts to college budgets are having a detrimental impact on the ability of colleges to maintain employee numbers, on staff morale, and on their ability to support students to develop the skills they most need in the workplace."

Labour's Iain Gray said: "The SNP record on colleges is simply shameful - budgets slashed, fewer students, falling attainment, inadequate student support and botched mergers.

"Nicola Sturgeon says that education is her top priority. She has put her best minister in charge and devoted plenty of warm words to it. It's now time to go beyond spin and fix her party's own record."

Liberal Democrat Tavish Scott said: "While the SNP are holding education photocalls with giant lumps of rock, the number of part-time students at Scotland's colleges has fallen off a cliff.

"These are the courses which benefit older people looking to retrain or those who cannot afford to study full-time. Fewer places means fewer opportunities."

Shirley-Anne Somerville, minister for higher education, said: "We have a strong track record on colleges. Since 2007, we have invested more than £550m in estates and maintained more than 116,000 full-time equivalent college places.

"Audit Scotland's report shows that the reforms have led to a 14% increase in people under-25 on full-time courses. Refocusing our resources on courses that will best prepare people to get a job was one of the major objectives of our reform programme.

"Since 2006/07, the number of women studying full-time courses in colleges is up by 16% and, as Audit Scotland notes, the gender balance in Scotland's colleges is broadly equal with women accounting for 52% of the student population (in 2014/15).

"Audit Scotland also highlights that Scotland's college sector is financially stable overall and exceeding its learning targets.

"This backs up this week's Scottish Funding Council report that calculated the costs of merger, £69.6m, are more than off-set by ongoing savings of £52.2m each year.

"This report helpfully highlights what is working well and we will consider its findings, including the more challenging conclusions, as we continue to deliver the job-focused learning that enables more of our young people to get the qualifications they need to get on in life."