Cumbria Constabulary investigated more than 200 coercive control allegations, but ended only nine with a charge or summons, figures show.
Home Office data shows that the force recorded 203 allegations of coercive control between April and September 2020.
Separate figures show that Cumbria officers assigned 125 outcomes to closed investigations in that time, just nine of which resulted in someone being charged or summonsed to court.
The new figures show that Cumbria Constabulary dropped 87 per cent of cases due to difficulties gathering evidence, with a further five investigations abandoned after being deemed not in the public interest.
However, the force has a higher rate of charges and summons than almost anywhere else in England and Wales.
Legislation was introduced five years ago to tackle the form of domestic abuse, but the figures show that the majority of allegations do not reach court.
The law is intended to protect victims of ‘extreme psychological and emotional abuse’ but Women’s Aid says it is clear “only a tiny proportion of survivors” see justice.
A review into the law’s effectiveness is currently underway, while the Home Office and the National Police Chiefs’ Council acknowledge there is work to be done to increase prosecution rates.
Abusers can be jailed for five years for subjecting a partner or family member to controlling or coercive behaviour, such as isolating them, exploiting them financially, depriving them of basic needs, humiliating or threatening them.
Just four per cent of 9,456 cases closed by police forces across England and Wales between April and September last year resulted in a charge or summons.
A Home Office spokesman called coercive and controlling behaviour “insidious”, adding: “We have worked closely with the police and prosecutors to ensure the law is used appropriately and since 2015 police recorded offences and prosecutions have increased year on year.
“However, we recognise there is more to do and we continue to work to identify the best ways to ensure the offence is properly understood and applied.”
For the offence to be prosecuted, there must be purposeful pattern of behaviour that has a serious effect on the victim and the accused must have known or ‘ought to have known’ that their behaviour would have had such an impact.
The new figures are likely to reflect a significant number of crimes that did not meet that prosecution threshold, according to Louisa Rolfe, assistant commissioner at the NPCC.
She said in such cases, officers work to safeguard victims and build cases should abuse worsen, adding: “This is still relatively new legislation and we are determined that we will use it effectively to better protect victims and bring dangerous offenders to justice.”
Lucy Hadley, of Women’s Aid, described the proportion of cases closed due to evidential difficulties as concerning, but acknowledged that gathering evidence in such investigations was a known challenge.
She said it was vital that “all judges, prosecutors and police officers truly understand coercive control and are confident in investigating, evidencing and prosecuting this crime.”
While the percentage of cases reaching court remains small, it has risen steadily since the introduction of the law, with around 600 magistrate court first hearings taking place between April and September 2020.
Forces recorded at least 13,692 offences in that time.