A coalition pledge to make hospitals share violent crime data with police is being carried out in only a third of areas in England, an audit shows.
The government has written to hospitals and chief constables for an explanation after the Department of Health audit.
Accident and emergency departments are meant to share information about where knife or gun attacks are happening with the police and local council.
This was part of the government's programme for government in 2010.
In 2010 the coalition promised in its programme for government to make hospitals share non-confidential information with the police so crime hotspots could be identified.
In the government's mid term report, which measured progress against their programme for government they said "we have established a national scheme requiring hospitals to share information on gun and knife crime".
But an audit carried out for the Department of Health has revealed that is happening effectively in only a third of community safety partnership areas, and not at all in one-fifth.
The charity Victim Support said it was very disappointing that the plan was not being implemented.
Susannah Hancock, its assistant chief executive, said: "The NHS is the second most likely public service after the police to come into contact with victims of violent crime, many of whom will not have reported such incidents to the police at all. "
It is thought that police are aware of fewer than a third of assaults that lead to the victim being treated in hospital.
Pioneering research carried out in Cardiff tested the idea of regularly sharing collated information about the type and location of attacks, with all confidential patient information removed.
As a result, the city saw a 35% fall in the numbers of assault victims turning up at A&E for treatment between 2000 and 2005.
Professor Jonathan Shepherd, from Cardiff University, said the research showed sharing information costs little, and saves money in the longer term for the NHS and the criminal justice system. He said the findings of the audit were surprising, giving the strong evidence, and the commitment from government.
"I feel disappointed that it hasn't been taken up faster than this, and I would want to say to hospitals and local authorities this is straightforward, ethical information-sharing that makes for safer communities - just get on with it."
Arrowe Park hospital, in the Wirral, has seen some impressive results from setting up systems to share information every month with the police and local council. Anyone arriving at A&E with an injury caused by a violent assault is taken through a standard set of questions about the location and circumstances of the attack.
The information has all patient data removed from it before it is shared. Between 2004 and 2010, the number of alcohol-related assault victims arriving for treatment fell by 30%.
Chris Oliver, from the Wirral University Hospital Trust, said the results had convinced busy staff in A&E to get involved: "It's owned by everyone within the department. The reception staff are very proactive when going through the questions. It's very rewarding for our staff to see the reduction in people coming into the department. It's a win-win."
The Department of Health said Health Minister Anna Soubry had written this week to all hospital chief executives and chief constables in England to remind them of the government's commitment on sharing information.
The letter says there are no legal reasons for not sharing anonymous information, and asks for any "good reasons why it cannot be done" in areas which have failed to put systems in place.
Despite this slow progress in implementing the approach in England, the idea has attracted international interest and there are pilot schemes under way in other countries.