By criminalising stalking, Cameron is making the right moves. But legal redefinitions alone won't solve the problem

A few years ago an academic I know had to suspend her career and go underground for a year. She was fleeing a stalker ? an ex-boyfriend who had spent three years following, messaging and threatening her.

She would wake up to dozens of texts and emails telling her the details of how he was going to attack her. He was blocked from her office email but constantly set up new accounts so that his threats would come through. She moved house but he tracked her down. He would wait in a car outside her flat to follow her to work, and outside her work to follow her home.

Eventually she gave up and fled the country. She spent a year doing low-paid secretarial jobs. It was the only way that she could be sure that her name wouldn't figure on any staff lists, and that her ex-boyfriend wouldn't be able to find her online. She hoped that if she vanished entirely his malevolent obsession with her would start to wane.

This woman was forced into exile because the legal system in the country she was living in, like almost every legal system in the world, was utterly uninterested in recognising or responding to the daily terror that she was being exposed to. The police told her they could only act once she was physically attacked. She could have sought an expensive civil injunction, but to do so she would have had to turn up in court, in full view of the man she was desperately trying to avoid, and give him the tremendous satisfaction of hearing just how effectively he had frightened her and damaged her life.

"That's everything he wants," she said. "To force me to see him, to hear how scared I am and how powerful he is ? that's just what he's trying to achieve." She decided not to when her solicitor told her that the police rarely arrested any man who broke such an injunction. It was a waste of time.

The official response to stalking in England and Wales has always been just as inadequate. There is no offence of stalking, only of harassment. The Home Office estimates that there are 120,000 cases of stalking every year, almost all of them consisting of men threatening women, and some of them ending in murder, rape and violent assault. On average, women endure a hundred incidents before they even report their cases to police. But they are rarely taken seriously. Sometimes they are told they ought to be pleased at the attention.

One woman showed police a series of terrifyingly graphic and obscene threats that she had been sent by a man she scarcely knew; they started laughing and reading them out to one another. Of those 120,000 cases, only 4% resulted in convictions in 2009, with just 735 sentences ? few exceeding six months.

Now that may be about to change. An independent parliamentary inquiry, set up last year to look at stalking, and which reported last month, came up with devastating evidence about its prevalence and its effects. A third of those stalked had full-blown post-traumatic stress disorder. Almost 90% of stalkers never had any action taken against them. Stalking was where domestic violence had been 30 years ago ? a huge problem that wasn't taken seriously.

There had to be legal change. Stalking needed to be made a specific offence. When Scotland did that in 2010, 150 stalkers were prosecuted in the first four months, and 90% pleaded guilty before trial ? contrasting with just 70 prosecutions over the previous decade.

The report was so powerful that David Cameron has decided to act. On Thursday he's expected to announce that stalking will be recognised as a crime for the first time and that serious cases will incur sentences of up to five years. That's to be commended, but campaigners worry that he won't go far enough.

Harry Fletcher of the probation union Napo, who helped set up the inquiry, believes the politicians are being stalled by civil servants who are reluctant to do more than fiddle a little with existing law. The team that deals with stalking at the Ministry of Justice has no sense of why action is needed on a wider front, he says, because its members have never talked to a single victim and have no idea of the complexity of the problem. He is worried that changes will be limited to naming stalking as a crime and making it imprisonable: legal redefinitions alone won't do.

What campaigners want is the promise of an entire bill dealing with the issue. Police and prosecutors must be trained to deal with stalking, so they act early to stamp on it; victims must be assessed for the risk they face, and given help to guide them through the system; and perpetrators must be given treatment in prison ? which doesn't happen at the moment ? so that they stop. The police need new powers. At present, for instance, they have none to arrest someone who has made threats and may be carrying equipment for kidnapping: rope, balaclavas and chloroform. That should be made an offence, just as going equipped for burglary is now.

If the prime minister doesn't come up with a comprehensive solution , then the campaigners have one waiting: a whole series of amendments that they have tabled for debate in the Lords next Monday, and that they will push to a vote if they are dissatisfied with the government's proposals. Stalking's victims have been ignored for too long to be satisfied by an inadequate response now.

Twitter: @jennirsl