Prison sentences being handed down to stalkers are so short that rehabilitation and treatment is impossible, campaigners have claimed.
About 20 stalkers a year are jailed for longer than 12 months for putting victims in fear of violence, the probation union Napo said.
Some were behind bars for just days, while others were sentenced to community orders and “inappropriate” domestic violence courses.
Calling for the law to be changed to tackle the problem of stalking earlier, Napo said tens of thousands of victims were being let down by the criminal justice system.
Shadow Home Secretary and Pontefract MP Yvette Cooper has committed Labour to the move, blaming a “lack of clarity” in the law for allowing stalking cases to escalate into still more “heinous” crimes against both women and men.
About 120,000 victims, mostly women, are stalked each year, but just 53,000 are recorded as crimes by police and only one in 50 of these lead to an offender being jailed, Napo said.
Harry Fletcher, the union’s assistant general secretary, said: “It is abundantly clear that if the criminal justice system does not intervene early to prevent stalking behaviour, then that behaviour escalated to violence and even murder.
“There is virtually no training for any criminal justice professional in understanding stalking and therefore it is no surprise that the response is so inadequate.”
Prime Minister David Cameron has said the Government would look at creating a new offence of stalking.
Last month, the Home Office announced a three-month consultation on the problem of stalking after victims complained of feeling “let down” by the justice system.
The world’s first clinic aimed at treating stalkers to help prevent violent crime opened in London earlier this month.
Official statistics show one woman in five and one man in 10 fall victim to stalking, a crime that can lead to murder, rape and sexual assault, the Barnet, Enfield and Haringey Mental Health NHS Trust said.
The National Stalking Clinic (NSC), which will assess stalkers referred by other agencies including the courts, police, probation service and the NHS, aims to tackle “murder in slow motion” and “psychological terrorism”.
One man who stalked his girlfriend by posting sexual pictures of her online for years without her knowing it was him was jailed for four months in October.
Ruth Jeffery, 22, said Shane Webber, had “wrecked the past three and a half years of my life”, adding that the sentence “will never make up for the hurt he has put me through”.
The actions of the unemployed 23-year-old from Nottingham “made me feel sick and so stressed because it was happening every single day”, she said.
A dossier of 80 cases by Napo also showed that most started stalking after the end of a relationship and there was evidence of domestic violence in three in four cases.