An unassuming low-rise building on a back street in central Bristol has been the venue for one British police force’s bold experiment to transform the way rape and sexual assault cases are handled.

Since April officers from Avon and Somerset Police, in the west of England, have been introducing a more sensitive approach aimed at reversing a steady slide in the proportion of complaints of rape and sexual assault that result in convictions.

Instead of concentrating on the credibility of the victim, police are urged to focus on understanding and investigating the behaviour of the alleged attacker.

Many of the most important conversations take place in the unmarked, backstreet building, known as the “Achieving Best Evidence” (ABE) suites. The facility is designed to put complainants of all ages at ease, with comfortable sofas where they can record their interviews, along with better support and understanding.

The programme — known as “Project Bluestone” — was cited on Friday as the likely template for a new approach to be introduced throughout the criminal justice system across England and Wales aimed at changing the investigation and prosecution of cases of sexual violence.

The government has faced particularly intense pressure over the issue because of the outcry that followed the disappearance and subsequent death in March of Sarah Everard. An officer in London’s Metropolitan Police, Wayne Couzens, has pleaded guilty to kidnapping and raping Everard while not entering any plea over a charge of murdering her.

The decline in the proportion of rape reports leading to prosecution became a focus of the wave of demonstrations that followed Everard’s disappearance. There were only 1,439 convictions for rape in England and Wales the year to March 2020, out of 55,130 reports. The system has struggled both with a surge in complaints spurred partly by the #MeToo movement and a shortage of capacity following a decade of austerity cuts.

On Sunday the justice secretary Robert Buckland said prosecutors and police would work closely together to “prepare the best possible evidence” adding that there would be a “real focus on the alleged perpetrators”. On Friday Buckland had apologised to victims of rape, saying the low conviction rates were “not good enough”.

Charlotte Leason, one of Avon and Somerset’s leads for Project Bluestone, said that, historically, much of the attention in investigations of sexual violence had focused on issues such as how much the victim had drunk. Academics advising on the project — led by Betsy Stanko, a criminologist who previously worked for the London Mayor’s office on Policing and Crime — challenged the force to look at the issues differently.

“What Betsy and her team have helped us to think about is how do we use intelligence to think about the suspect’s behaviour,” Leason said. “Was this [attack] targeted? Was [carrying out the attack] their motive in going out that evening?”

The approach also sought to reduce the pressure on victims, Leason added. Complainants were often pressed to provide all their evidence quickly, to check whether it would stand up in court. The pressure can prompt victims to withdraw co-operation.

“The challenge now is to ensure we put victims more at the heart of our process and ensure they have the support and time to provide their evidence in a way that feels comfortable and appropriate,” Leason added.

Even some people who normally criticise police forces’ record on sexual violence are supportive of Project Bluestone.

Andrea Simon, director of the End Violence Against Women Coalition, said the initiative had been “incredibly valuable” because the academics had undertaken a full audit of what was going wrong.

“Moving to a suspect-centric approach, where the history of someone’s offending and their background is given more weight, would improve the experience of the justice system for victims and take investigations in a different direction,” Simon said.

At the ABE suites, one officer involved in applying the new approach, Kate Douglass, said the force had sought to cut the time after a complainant’s initial report before officers conducted the first interview. Because of the pressure on resources, the force had previously often left a considerable gap before interviewing the growing number of people reporting historic sexual offences.

“Irrespective of whether this crime was committed 50 years ago or two hours ago, they’re still living through it,” Douglass said.

Richard Marsh, a detective inspector involved in the process, said Stanko and her team suggested officers had become too exhaustive about disclosing to defence teams absolutely everything potentially damaging to their case that they found on victims’ telephones.

The process of disclosure of evidence found on mobile phones has helped to generate significant new delays before cases come to court, causing many victims to give up.

“What the academics are saying is we’ve gone too far down the line of finding anything at all that looks bad in any light for the victim,” Marsh said.

Yet the question facing the Bluestone approach is whether it will produce results as it is tested in further pilot studies then, potentially, rolled out across England and Wales.

Simon said funding was one potential problem. The government has said it wants to conduct more pilots in more areas over two years but has provided only one year’s funding to do so.

“At this point, for the majority of rape victims to have to wait several more years for an improved national response to rape investigations feels far too slow a pace of reform,” she said.

Nevertheless, prosecutors said they were pleased with the project’s progress. Victoria Cook, Chief Crown Prosecutor for CPS South West, said the focus brought by Project Bluestone had resulted in “a closer working relationship between the police and the CPS”.

Staff at The Bridge, an NHS-run sexual assault referral service at Bristol’s Central Health Clinic, also pointed to encouraging signs. They said there had been improvements in communication by police officers with victims, who are often referred to the service by police officers for a medical examination to provide evidence.

The service also accepts patients referred directly from medical practitioners and tracks its “referral rate”, the proportion who feel confident, after contact with staff, to pursue a criminal complaint.

Nicola Shannon, The Bridge’s service manager, did not give precise numbers for how the referral rate had changed and was careful about attributing changes entirely to Project Bluestone.

But she said: “What we’ve noticed is that in March and April and May and June our referral rate has doubled. So something has changed.”