Campaigners against sexual violence have renewed calls to abolish the controversial Scottish verdict of not proven as the UK’s largest mock jury study reveals that the availability of this option may push more jurors towards acquittal before they have even discussed the evidence.

Welcoming the landmark research, Scotland’s justice secretary, Humza Yousaf, said whether to move from a three- to a two-verdict system was central to further consultation on reform.

The Scottish legal system has a number of unique features – including the three-verdict system and the requirement for corroboration – which are thought to impact disproportionately on rape and sexual assault cases, leading to markedly lower prosecution and conviction rates.

Not proven is one of three options available to a jury or court along with guilty and not guilty. It leaves the accused innocent in the eyes of the law but critics argue it is confusing for juries and the public.

The comprehensive study, presented in Edinburgh on Wednesday, discovered that during deliberations jurors viewed not proven as a “compromise” verdict, meaning “guilty but you can’t prove it in court”.

Miss M, who won a landmark civil action after the criminal case against the man she accused of raping her on a university freshers’ week night out was found not proven, has been campaigning for reform of the Scottish system for nearly a year. “This must add to the momentum,” she told the Guardian. “This research shows that not proven is failing survivors.”

The research, commissioned by the Scottish government and involving 64 mock juries and nearly 1,000 participants, also found that the existence of the not proven option had an impact on jurors independent of deliberations, suggesting that removing it might incline more jurors towards a guilty verdict.

It concluded that individual jurors were also significantly less likely to favour a guilty verdict when the not proven verdict was available, a difference that was apparent both before and after deliberating “indicating that, in finely balanced trials, the availability of not proven may tip more jurors towards acquitting even before they have discussed the evidence”.

The two-year study, carried out by Ipsos MORI Scotland Prof James Chalmers and Prof Fiona Leverick of the University of Glasgow law school and Prof Vanessa Munro from the University of Warwick, followed the deliberations of each jury after they watched a video of a fictional but realistic Scottish trial, either concerning a rape or an assault.

It also examined other elements to the Scottish jury system that differ from most English-language jurisdictions: including having 15 members rather than 12, and that verdicts are returned by simple majority, ie eight out of 15 jurors, rather than requiring juries to reach unanimity or near unanimity.

In 2017-18, only 10% of reported rape and attempted rape cases were prosecuted in Scotland: of these 43.3% resulted in convictions – the lowest of any crime – while 19% were found not proven, compared with 17% for all crimes and offences.

Responding to the research, Sandy Brindley, the chief executive of Rape Crisis Scotland, said: “This research shows a significant level of misunderstanding about the not proven verdict. It’s time for it to go, before more guilty men walk free.”

She said she wanted the Scottish government to take a broader look at how the legal system served victims of sexual violence, including the requirement of corroboration – two separate sources of evidence before a case can proceed to trial – which is especially difficult for rape prosecutions where the accused argues that the sexual activity was consensual.

“The biggest impact of corroboration is preventing cases getting to court in the first place. At the very least we want to get rid of not proven, but given what we know about low conviction rates and how traumatising the court experience is for victims, it’s time for a more transformative change.”

Yousaf said the study would be subject to a targeted consultation over the winter with judges, victims’ groups and others.

He said “nothing is off the table” in terms of potential reforms, adding: “Central to these discussions will be whether we should move from a three- to a two-verdict system.”