December marked the sixth anniversary of landmark legislation introduced to make coercive or controlling behaviour a criminal offence in England and Wales.
But only a "small minority of survivors" who experience such abuse will see justice done, according to charity Women's Aid.
Data published by the Office for National Statistics shows Sussex Police logged 1,031 allegations of coercive or controlling behaviour during 2020-21.
That was down from 1,247 the year before – but different figures suggest most cases will never reach a courtroom.
Of the 839 cases closed by the force in Sussex during 2020-21, 93% were abandoned due to difficulties gathering evidence while just 19 ended with a suspect being charged or summonsed to court.
Women's Aid described coercive control, which is punishable by up to five years imprisonment, as a problem "at the heart of almost all domestic abuse".
Abusers can be jailed for subjecting a partner or family member to controlling behaviour such as isolating them, exploiting them financially, depriving them of basic needs, humiliating, frightening or threatening them.
During the first year of the pandemic, 34,000 allegations were reported to forces across England and Wales, with the number of recorded crimes rising by more than a third compared to around 25,000 in 2019-20, though data for that year excludes Greater Manchester Police.
Home Office figures show more than nine in 10 investigations closed nationally in 2020-21 were dropped due to evidential difficulties, while just 4% resulted in a charge or summons being issued.
Charge rates differed significantly between police force areas and were highest in South Wales, where 14% of cases resulted in a charge or summons and lowest in North Wales, where just 1% of cases did.
In some cases, prosecutors and investigators may close a coercive control investigation but continue to pursue other offences linked to the case.
Isabelle Younane, head of policy, campaigns and public affairs at Women's Aid, called for consistency between forces and said it is vital all police officers and prosecutors understand the nature and "damaging, lifelong impact" of coercive control.
She added: “Survivors need, and deserve, a consistent response to their experiences of abuse."
"It is a matter of urgency for the Government to invest in multi-agency and partnership working across services."
A spokesman for the National Police Chiefs' Council said the response to the complex problem had improved in recent years but acknowledged the need for better understanding across the justice system.
He said officers sought to safeguard victims and build cases where reported incidents meet the requirements to be considered a crime but not the threshold for arrest or prosecution.
A Home Office spokeswoman said the Government is acting to tackle the "particularly insidious" form of domestic abuse and will publish its Domestic Abuse Strategy this year.
She said police forces are expected to take allegations seriously, adding: "The increase in reporting of these crimes shows the improvements the police have made, with victims more willing to come forward."