Scots from disadvantaged areas face a "shocking access gap" and are four times less likely to go to university than those from wealthier backgrounds, researchers have found.

A report from think tank the Sutton Trust found 90% of growth in higher education places for disadvantaged students in Scotland in the past decade comes from colleges, not universities.

The trust is now calling for the urgent appointment of a new independent commissioner for fair access to tackle the problem.

Trust chairman Sir Peter Lampl said: "Scotland faces a shocking access gap and it is vital that the government appoints a strong independent commissioner without delay.

"There is good practice in Scottish universities on access but we need a really strong push if talent is not to be wasted."

Analysts found Scots are more likely than their English counterparts to enter higher education but are less likely to go straight to university, and half who go via college repeat at least one year.

In 2013-14, more than half (55%) of Scots entered higher education by the age of 30, 34.1% straight from school and 20.9% going to college first. In England, 46.6% entered higher education, with just 6% starting at colleges and other non-university providers.

The study found Scots from disadvantaged areas are more likely to attend leading universities than their counterparts in England, however, credited to the Scottish Government's funding of places at the ancient universities for poorer students.

Professor Sheila Riddell, who led the study, said it highlighted the "over-reliance on the Scottish college sector to increase participation rates overall" and the failure of Scottish university places to keep up with increasing demand.

She said: "Despite free tuition, the Scottish university sector has much work to do in order to realise the goal of fair access."

A spokesman for industry body Universities Scotland warned comparisons between Scotland and England are "not always meaningful" due to differing education systems.

He added: "What is clear from the Sutton Trust's analysis is that England's policy of uncapped places has made it easier to get into university and this has helped access.

"Scotland's strict cap on places has made it much harder for Scottish students to get into Scottish universities. This is having clear knock-ons in terms of entry requirements and access."

Tory shadow education secretary Liz Smith also criticised the capped places policy and said the limited progress in Scotland partly reflects lower bursaries.

She said: "These are both matters for the SNP to address urgently, most especially in light of its policy to force universities to take 20% of their intake from disadvantaged communities by 2030, and because of recent reports which shine a light on the dangers of Scottish universities lagging behind in the finance that needs to underpin cutting edge research and innovation."

NUS Scotland vice-president Rob Henthorn said Scotland should not be "ashamed" of college access to university as it is a welcome alternative for many but he warned it would become a "scandalous missed opportunity" if universities fail to encourage students to use their college qualifications as a route to achieving a university degree.

He added: "The evidence of this report, and the commission, suggests there is still a two-tier system in place.

"Countless students are forced to repeat years of study - a waste of time, money and potential - or not even having their college qualifications recognised."

A Scottish Government spokesperson said: "Access to university for students from the most deprived areas has increased by 29% since this government came to office. The Sutton Trust report acknowledges that progress has been made on widening access, however we are clear that there is much more still to do.

"That is why we introduced the Commission for Widening Access and have committed to implementing in full its recommendations. Indeed, the recommendations set out by the Sutton Trust are already being taken forward in Scotland following the Commission's report.

"However, some of the report's findings are based on misconceptions that do not accurately reflect the position as regards widening access in Scotland."

"For example, it is simply wrong to state that university places supported by additional funding will end in 2016/17. In reality the places will be mainstreamed into core funding and the higher education sector agreed to this at the outset of the initiative.

"The Trust's argument on additional places also fails to acknowledge the Commission's finding that simply supplying additional places does not address the systemic problems that can restrict access."