By Dominic Casciani
BBC News Home Affairs
Eighteen forces reported increases in the category of "most serious violence"
Eighteen police forces asked to recount some of the most serious violent crimes amid a row over accuracy have been named by the Home Office.
The list shows that forces were asked to clarify data amid confusion over the definition of a serious attack.
Last year the Home Office was forced to revise national figures on some serious violence - leading to a 22% jump in incidents compared with 2007.
Police forces say they are not to blame for a mistake based on ambiguous rules.
The Home Office asked the following forces to recount some of their most serious violent offences: Bedfordshire, Cambridgeshire, Cumbria, Derbyshire, Essex, Hertfordshire, Kent, Lancashire, Norfolk, North Wales, North Yorkshire, Suffolk and Thames Valley.
Five other forces - the Met, Cleveland, Staffordshire, Humberside and Nottinghamshire - were asked to take part but did not provide revised data.
The row over categorisation of some serious violence began when police chiefs noticed that some forces were reporting figures out of step with what had been expected.
The problem emerged in October 2007 and concerned how some officers were recording some incidents of grievous bodily harm.
Some of these incidents, such as an attack in a pub with a broken glass, were not being classed as the most serious category of violence, because the assailant had only inflicted a minor injury.
However, other forces were categorising similar incidents as the more serious offence of grievous bodily harm with intent, because the attacker had clearly wanted to cause immense harm to the victim.
The confusion, say police chiefs, came down to the ambiguous nature of a key part of the guidelines used by officers to class crimes prior to prosecutions. All forces involved in the recount have denied deliberately or knowingly miscounting or downgrading violence.
The mix-up led Home Office experts to stop calculating levels of the most serious violence while figures were double-checked.
Police chiefs are said to be privately furious at the fiasco, feeling that some forces are being accused of under-counting violence when all their officers were doing was following national guidelines on how best to categorise offences.
A spokesman for the Association of Chief Police Officers said: "There is no suggestion that forces have not been ethically recording violent crime.
"The Home Office picked out 18 forces as a way of drilling down into some of the areas where statistics had been particularly affected by the change to the counting rules to better understand the impact of those changes.
"That does not mean those forces were recording in a different way to others. All police forces record crime according to their best understanding of guidance provided.
In a statement to the BBC, Detective Chief Superintendant Iain Goulding of Cumbria Constabulary said just four of 833 incidents of serious assault in his area had been wrongly classified between April and June 2008.
"This is a technical matter and does not impact on quality of service delivered to victims," he said.
"Each and every case was fully investigated and we have some of the highest detection rates in the country for solving violent crime.
"Violent crime continues to fall and Cumbria remains one of the safest places to live, work and visit."
A spokesman for Essex Police denied that its officers had been undercounting offences. They had been following Home Office guidelines, she said.
Neighbouring Hertfordshire Police confirmed it had misinterpreted guidance over classification - but said it had been over-recording serious violence.
And Kent Police said the crimes covered in the recount represented only 6% of all violence it had recorded.
"Kent has put in place robust procedures to ensure that how we record this category of crime reflects the Home Office changes and rather than under-recording these offences we have been identified by the Home Office, along with a number of other forces, as over-recording serious violent crime.
"We have already raised the current difficulties in consistently interpreting the revised guidance with the Home office along with other forces."