Temperatures at night in Liverpool have fallen as low as -16C this week, but that hasn't deterred the city's street sex workers from going out to earn enough money for their next fix of drugs.

"You never know when you get into a car with a man whether you're going to be raped or paid," said Julie, a woman in her 40s who has sold sex on the streets of the city intermittently for more than two decades.

Similar scenarios are repeated across the UK. But something different is happening in Liverpool. Between 2000 and 2005 there were six sex worker murders in the city, two of them still unsolved.

Liverpool had the highest sex worker murder rate after London and Glasgow, and police decided that something radical had to be done to reverse the trend.

They realised that sex workers had a wealth of intelligence about violent criminals, but for as long as they mistrusted the police they wouldn't pass it on.

So the police began to build links with projects supporting sex workers, notably Armistead, an NHS project providing support and healthcare to sex workers, which is part of Liverpool community health NHS trust.

While minor offences such as soliciting are still pursued, the police shifted their focus to protecting sex workers and building relationships of trust with them.

In 2006, Merseyside police was the first and so far only force in the country to declare crimes against sex workers as "hate crime".

The results have been dramatic. In the five years before the new way of working began to take effect in 2007, there was just one conviction for a series of assaults against sex workers.

Now the overall conviction rate for crimes against sex workers is 84%, with a 67% conviction rate for rape. The national average conviction rate for rape is just 6.5%.

Last year in Liverpool there were 10 convictions for rape and several more men have been charged and are awaiting trial in 2011, some for multiple rapes as well as other violent offences.

Detective Superintendent Tim Keelan said: "These women are very vulnerable, and our priority is to protect them. We are seeing interest from a number of other police forces in our model and we have set up a Unity team – the only joint police and CPS team in the country – to help prosecute offenders."

Julie was a victim of rape earlier this year and is deeply traumatised by what happened to her. Her evidence has helped to charge her attacker with rape.

"I thought I was going to die during the attack. Since I reported the rape, I've had so much support from the police and Armistead. Without them I don't think I'd be able to go through with testifying when the case comes to court, because I'm absolutely terrified of facing that man again."

"Sadly, this model isn't being replicated in many other areas of the UK," said Rosie Campbell of the UK Network of Sex Work Projects. "The proactive approach we're seeing from Merseyside police is needed across the UK.

"Many of the laws surrounding sex work make it difficult for sex workers to trust the police. Soliciting laws directly criminalise them so the people who are there to protect them can also arrest them."

Armistead, in common with other sex-work projects, uses a system of "ugly mugs" where women can report attacks and give a detailed description of their attacker. With their permission this information is passed on to the police.

Ugly mug reports in Liverpool have been key to catching offenders. But these reports, which contain vital intelligence, are not shared nationally. As a result, crucial information about offenders who move around the country is missed.

The Association of Chief Police Officers is backing calls from the UK Network of Sex Work Projects to make the system national. Members of the network are about to submit research to the Home Office about the benefits of making the scheme national.