For decades survivors have been reporting that the most difficult thing about domestic abuse is not necessarily the physical violence: the bruised ribs, chipped teeth or broken bones.

The worst part, many survivors say, is the psychological abuse — the manipulation and surveillance, the gradual isolation from friends and family, the rigid rules, degrading put-downs, humiliation and threats — the insidious "system" of behaviours perpetrators use to dominate and entrap their victims known as coercive control.

Sometimes referred to as "intimate terrorism", coercive control chips away at victims' sense of safety and independence; some report feeling as if they're being held hostage, constantly "walking on eggshells" or being "smothered alive".

"The most distressing thing I lost was me, my [self-worth]," one female survivor told Victoria's Royal Commission into Family Violence in 2016.

"Couldn't think straight, even to the point I couldn't write out a shopping list: I couldn't concentrate. I was always worried that I may do or say the wrong thing. It is so hard to describe to you the mental torment, always questioning yourself. Never being able to comprehend that this person who is supposed to love me can hurt you so badly."

It can also be a warning sign.

Professor Evan Stark, a sociologist who developed the concept of coercive control, has defined it a "pattern of domination that includes tactics to isolate, degrade, exploit and control" victims, "as well as to frighten them or hurt them physically".

Stark's research has found 60-80 per cent of women who seek help for abuse have experienced it, and that the "level of control" in such relationships is a predictor of severe and fatal violence. A review of domestic violence-related homicides in NSW, for instance, found that in 99 per cent of cases, the relationship was characterised by the male abuser's use of coercive controlling behaviours towards the victim.

But coercive control is not a crime in Australia, and unless a perpetrator has stalked or physically assaulted someone, damaged property or breached an intervention order, they are unlikely to be detected or punished. And some domestic violence workers are concerned too many victims are falling through the cracks in the legal system and remaining in dangerous situations as a result.

"I don't think just criminalising coercive control is the only answer, it's not going to fix the problem of domestic abuse," Jess Hill says. ( Jack Fisher (ABC) )

For this reason, some countries have introduced legislation that makes it a crime to commit coercive controlling behaviours against an intimate partner: England and Wales were the first to do so in 2015, with Scotland's "ground-breaking" Domestic Abuse Act — which creates a "course of conduct" offence allowing physical, psychological and coercive behaviours to be prosecuted at once — coming into force in April this year.

Now experts are urging that similar laws should be introduced in Australia, and that cases being prosecuted in the UK should give policymakers confidence the approach can work here, too. Criminalising the seemingly "invisible" behaviours at the heart of so many abusive relationships, some researchers say, would completely reshape the way authorities understand and respond to gendered violence and better hold perpetrators to account.

Could criminalising coercive control 'backfire' on victims?

"At the moment we see physical violence as the most damaging, and yet we know that long term, especially for children, being in a coercively controlling household can create the same lasting harms as direct physical or sexual abuse," said Jess Hill, the author of See What You Made Me Do, a bestselling book about domestic abuse.

Victims experiencing threatening or frightening behaviours can apply for a protection order but in many situations, she said, civil action is not enough. "For that kind of behaviour to be invisible to the eyes of the law is reprehensible ... why wouldn't we at least seriously consider making it a crime?"

Several inquiries have already examined the question, including the Australian Law Reform Commission in 2010, Queensland's Special Taskforce on family violence in 2015, and Victoria's Royal Commission into Family Violence. All recommended against introducing new laws, though, in part because they found they often only have a "symbolic effect" and do not result in actual change.

Some advocates and criminologists remain concerned the behaviours would be too difficult to define and prosecute (where is the line between "unpleasant" and criminal behaviour?) and potentially even backfire on victims.

There is a risk that if coercive control was criminalised, female victims may be misidentified as perpetrators by police, says Helen Matthews. ( Supplied: Vanessa Shambrook )

"There is still a struggle to get people to recognise coercive controlling behaviours as family violence ... and certainly people are falling through the cracks of the system," said Helen Matthews, director legal and policy at the Women's Legal Service Victoria. "But I'm not sure that by criminalising coercive control we are actually dealing with what I would prioritise as the needs of those victims."

Many women experiencing domestic abuse don't necessarily want the perpetrator to be punished, Ms Matthews said, or to be pressured into providing evidence to a criminal process: doing so, she said, could result in a loss of financial support, disrupt their children's relationship with their father, or escalate his use of violence.

There is also a risk, she added, that women may be misidentified as the perpetrator of abuse by police, who tend to take an incident-based approach and focus on gathering evidence of physical violence offences. This can mean a perpetrator's broader pattern of abuse — and its impacts on the victim — are overlooked.

"We see women who are readily charged by police with assaults after they have lashed out after enduring periods of coercive control," Ms Matthews said. On the flipside, she said, in too many cases police are not pursuing criminal charges when abusers have used physical violence. (As ABC News recently reported, this is a particular concern for Aboriginal women, who are massively over-represented in the domestic violence protection order system and prison population).

"We really need a more consistent and informed response from police in the use of their existing powers before we extend those powers to areas which require a high level of discretion and understanding of family violence."

In the UK, a range of behaviours are being prosecuted

But the authors of a new study that looked at how the offence is being used in England and Wales say there is no evidence to show some of those concerns are playing out.

As part of the research, published in the journal Criminology and Criminal Justice, Deakin University's Paul McGorrery and Marilyn McMahon analysed media reporting of the cases of 107 defendants convicted of coercive controlling behaviours to understand what kinds of offenders, relationships and behaviours were being captured.

"The key finding above all else is that, contrary to some concern that the offence could be misused against women, 106 out of 107 convicted offenders ... were male — that's more than 99 per cent," Mr McGorrey told ABC News. This is consistent with statistics published by the UK Ministry of Justice, which reported that 97 per cent of offenders sentenced for the offence in 2017 were male.

In the majority of convictions analysed, the offender was reported as having committed some kind of physical or sexual violence against the victim. ( Flickr: Hibr )

The one case in the study involving a female offender and male victim, Mr McGorrery said, was a "genuine case of coercive control" in which the court accepted evidence that, over a period of seven years, the woman had stabbed her boyfriend, scalded him with hot water, made him sleep on the floor, isolated him from family and friends and controlled his Facebook account.

"But the media was so fascinated by it ... [perhaps] because it broke the trope. And unfortunately because of that interest it gave far too much oxygen to arguments that coercive control is not a gendered phenomenon. The fact is, it is gendered but there are exceptions."

The research also identified a range of behaviours being prosecuted. Many offenders threatened to kill their victim, themselves, or a victim's pet (one killed his partner's cat; another threw the victim's kitten against a wall), while others committed "degrading" acts including urinating on the victim or stripping her naked and throwing her clothes out the window.

There were dozens of other cases where offenders prevented victims from leaving the house, working, or from seeing friends and family, while many controlled or monitored their partner's use of phones and social media. "The depravity of men in these relationships always shocks me," Mr McGorrery said, "but doesn't surprise me."

In the majority of cases analysed, the offender was reported as having committed some kind of physical or sexual violence against the victim, including strangulation, punching, and attempted drowning — some of which could have been charged under existing laws.

That could mean abuse is being reported and or charged only when it involves physical violence, Mr McGorrery said, which would be missing the point of the offence. Or, "that Evan Stark is quite right, that ... most relationships underpinned by coercive control have at some stage involved one or more incidents of actual or threatened violence."

Survivors are saying, 'It's about damn time'

That is not to say the English offence is working perfectly: other research has found police may be "missing key opportunities" for identifying patterned abuse and that the offence is not being used to its "full potential".

Prosecutions and convictions have remained consistently low: by March 2018 police had recorded 9,053 offences of coercive control but as of December 2018 there had been just 235 successful convictions, with police forces reporting charges were "challenging to prove".

"I've done a lot of training with police officers and while some really get it, some really just don't," Jane Monckton-Smith, a former police officer and criminologist at Gloucestershire University, told the Bureau of Investigative Journalism in 2017. "They have this resistance and see it as women just whinging, there is that feeling that it is not dangerous. They just don't get how serious it is, they think it is just we have to criminalise people for calling people names when that is not it at all."

The voices and experiences of victim-survivors have been reflected in Scotland's new domestic abuse laws, says Dr Marsha Scott. ( Supplied: Scottish Women's Aid )

Which is why many experts are now looking to Scotland, which in April enacted laws Evan Stark has described as "gold standard". Unlike laws in England and Wales, Scotland's domestic abuse act puts the focus on perpetrators, not victims: prosecutors must demonstrate a person has engaged in an abusive course of behaviour intended to cause harm, not necessarily that the victim was seriously affected by it.

It also includes offences against current and former partners regardless of whether they are living together, as well as children. And while England's maximum penalty is five years' imprisonment, Scotland's is 14 years.

Crucially, says Marsha Scott, the chief executive of Scottish Women's Aid, there has been a huge investment in training police officers, sheriffs and judges.

"It was an incredible breakthrough," Dr Scott told ABC News. "We were pleasantly surprised at how quickly we were starting to see cases in the courts ... we thought it would take a while but it was a matter of weeks before the first case was in court."

She partly attributes its early success to the careful and consultative development of the bill, which was passed unanimously. "The only 'no' vote was apologised for later, because it was from the chair of the justice committee who didn't have her glasses on and pressed the wrong button."

In the first three months, Police Scotland logged more than 400 crimes, and Dr Scott said there had been about 100 convictions to date. "It's early days ... but overall the attitudes and feelings of survivors is, it's about damn time.

"That doesn't mean they don't have criticisms about ... their treatment in court or parts of the system that still need improving. But what they are saying is, this is so much closer to my experience than anything that has been in the law before."

'We don't want to just be contributing to the prison population'

Criminalising abusive behaviours that can cause victims to feel "trapped" may also improve legal outcomes for women charged with homicide: as ABC News reported recently, some legal academics are now arguing that evidence of coercive control and its impacts on women who kill abusive partners can be crucial for supporting claims of self-defence.

This may have been the case for British woman Sally Challen, who in 2011 was convicted of murder after she bludgeoned her husband to death with a hammer. Challen walked free from prison in June after successfully appealing her conviction, with judges finding she had been suffering from a psychological condition at the time of the killing — the result, her lawyers argued, of years of coercion and control by her husband.

In Australia, some experts are also questioning the impact criminalising coercive control might have on offenders.

"If we do introduce these offences we really have to think about the appropriate penalty response; we don't want to just be contributing to the prison population ... because for most people prison is a very destructive place," said Heather Douglas, a law professor at the University of Queensland.

"There is possibility for extraordinary creativity within sentencing statutes across the country," she said — for example, sentencing offenders to community corrections orders or mandating participation in behaviour change programs. "But there is currently a lack of resources for those alternatives."

Jess Hill agrees it's important any change in law is accompanied with support for abusers and the organisations that assist them.

"Police are not perfect, laws don't change culture," Ms Hill said. "I don't think just criminalising coercive control is the only answer, it's not going to fix the problem of domestic abuse. We need to be pairing that with things that actually work to change behaviour or heal people who are exacting this type of violence."

But the threat of punishment can be a strong deterrent, says Paul McGorrery, and sends a message to the community about what behaviours are unacceptable. The "symbolic effect", in other words, can make a significant difference.

"One of the key things it does is it tells offenders, 'the state doesn't sanction this behaviour' — to the point where we'll actually employ the criminal law if you're caught doing it. And it tells victims, 'you don't have to tolerate this behaviour ... it's so wrong that if you report it, police will be on your side and ... intervene on your behalf'," he said.

"The reason to criminalise coercive control is because ... the alternative is to expect women to continue to bear the burden of this abuse privately."