Just over a year ago the charity Protection Against Stalking (PAS) and Napo, the probation and family court union, launched a campaign to raise awareness of the consequences of the stalking of women. Who would have thought that by April 2012, stalking ? involving the fear of violence and psychological harm ? would become an offence on the statute book. How did we do it?

The two organisations first met at an Association of Chief Police Officers meeting, which was reviewing stalking and harassment law and training. It was clear that the law was inadequate, the training of professionals was, at best, piecemeal and victims' advocacy was non-existent. It was evident, too, that existing legislation passed in 1997, the Protection from Harassment Act, was no longer fit for purpose.

A decision was taken to raise awareness in Westminster. An early day motion was tabled, calling for stalking law reform and for the first ever National Stalking Awareness Week.

The campaign then set up an independent parliamentary inquiry and invited Elfyn Llwyd MP, chair of the justice unions' parliamentary group, to chair it. PAS and Napo acted as advisers to the inquiry, helping to draft its terms of reference. We approached MPs and peers across parties to sit on the inquiry, and victims ? including mothers whose daughters had been killed by stalkers ? academics, lawyers and frontline police and probation officers to give evidence.

The inquiry heard about campaigns of intimidation and fear, many of which had lasted for years. In all cases the response of the criminal justice authorities was at best haphazard and at worse indifferent. By the time of the launch in February in the House of Lords of the inquiry's final report, which we compiled alongside a draft stalking bill, more than 60 MPs and peers had been recruited to the cause, along with organisations from the Police Federation to the Magistrates' Association.

At the same time as our campaign, the protection of freedoms bill was going through parliament. At a Labour peer's request, we added amendments that created a stalking offence and made it a criminal offence as well as a civil one.

On International Women's Day, 8 March, the prime minister announced support for law reform. But the following day the government published its own amendments to the bill, which limited the definition of stalking to "a fear of violence". There was no mention of psychological harm. There followed 72 hours of negotiation and lobbying, after which the government agreed to include a clause on fear and anxiety and psychological harm.

The bill will become law on 24 April, after which there will be a six-month period of consultation on training and sentencing guidelines. In November, the new law will become operational.

Our success was achieved in a remarkably short time. The key was all-party support for the independent inquiry, where victims' voices were heard and frontline practitioners were taken seriously; a wide range of organisations backing the campaign; the individual lobbying of MPs and peers; and support of political parties. It was time-consuming and intense, with more than 20 detailed briefings and dozens of press releases produced, but it worked.

But the job is not yet finished. The physical violence and psychological harm caused by stalkers remains unacceptable; the priority now is obtaining funding for a victims' advocacy scheme.

? Harry Fletcher is assistant general secretary of Napo, and Laura Richards is co-founder of PAS