A scheme giving women the "right to know" if a partner has a history of domestic violence is being launched.
The pilot scheme is also known as Clare's Law after campaigning for a change in the law to help protect women by Michael Brown, the father of a murder victim.
His daughter, Clare Wood, was strangled and set on fire by her ex-boyfriend George Appleton at her home in Salford, Greater Manchester, in February 2009.
Appleton, dubbed the "Facebook Fugitive", then went on the run before hanging himself.
Miss Wood, 36, a mother of one, had met Appleton on Facebook, unaware of his horrific history of violence against women, including repeated harassment, threats and the kidnapping at knifepoint of one of his ex-girlfriends.
At the inquest into Miss Wood's death last year, Coroner Jennifer Leeming said women in abusive relationships should have the right to know about the violent past of the men they were with.
The family's campaign was also taken up by Salford and Eccles MP Hazel Blears and backed by police and Home Secretary Theresa May, who agreed to run the pilot.
Ms Blears said: "Following the tragic death of Clare Wood, who was a resident in Salford, I have worked closely with her father and family to gain cross-party support for 'Clare's Law'. Too many women and men continue to suffer domestic violence and it is vital that all possible steps are taken to protect people and to provide them with the information they need to make an informed decision."
Information may be disclosed via a request from a member of the public, the "right to ask", or by an agency where a decision is made to consider disclosing the information in order to protect a potential victim - the "right to know". If police checks show that a person may be at risk of domestic abuse from their partner, the police will consider disclosing the information.
The initiative, officially called the Domestic Violence Disclosure pilot scheme, will run in Greater Manchester, Gwent, Wiltshire and Nottingham until September 2013. Home Office Minister Lynne Featherstone, who will attend the launch in Greater Manchester, said: "Domestic violence is a dreadful crime which sees millions of women and families suffer years of abuse."