Sweeping changes to the make-up of police forces in England and Wales have been recommended in an official report.
Some senior officers want a single national force
The existing structure of 43 forces is "no longer fit for purpose", the Inspectorate of Constabulary said.
Some smaller forces should be merged so they meet the needs of 21st Century policing and provide the standard of protective service necessary, it said.
Home Secretary Charles Clarke said he would consider the report carefully before giving a response.
"I look forward to productive discussions on the best way forward," he said.
'Efficiency and effectiveness'
Inspector of Constabulary Denis O'Connor, who is a former Surrey chief constable, criticised the number of forces currently in existence.
He said: "In the interest of the efficiency and effectiveness of policing it should change."
But some forces have expressed concern at the report's proposals.
Ian Roberts, chairman of North Wales Police Authority, said he did not want the four Welsh forces to be "lumped together" as his area would become "isolated".
He said: "Logistically, north Wales and south Wales are poles apart. We've got a large stretch of mountains between us and it takes three hours to get down there."
Mr O'Connor said forces with more than 4,000 officers tended to perform best and that reorganisation could save up to £2.3bn over 10 years.
At present 19 have fewer than 2,000 officers, with senior officers admitting that some struggle to meet the challenges of modern crime.
Former Home Secretary David Blunkett proposed the creation of larger "strategic" forces big enough to deal with the demands of modern policing.
Reforms in 1967 saw the number of forces cut from 300 to the current level of 43.
But Rick Naylor, president of the Police Superintendents' Association, said reducing the number again to about 30 would not be going far enough.
"We want to see a single national police force, with existing basic command units providing local policing," he said.
"The question is whether the government have the political bottle to go down this radical road."
With 30 forces, there would still be some without "the resilience to deal with all the facets of modern policing", he added.
Chris Fox, president of the Association of Chief Police Officers (Acpo), welcomed the report, saying: "All forces must have the capability to deal with terrorism, cross-border and international crime if we are to keep the public safe and give them the service they expect and demand."
But he warned restructuring would be "complex and expensive". He said Acpo and other policing bodies would be meeting the home secretary on Monday to discuss how to take the report forward.
Shadow environment secretary Oliver Letwin, whose local Dorset force looks a likely candidate for a merger with neighbouring Wiltshire or Hampshire, told BBC News the proposals were "undiluted rubbish".
"The main problem about policing in Dorset, and I suspect it's very similar in most other rural counties in England... is the people feel the police are remote."
He said police needed local knowledge to deal with the low-level crime affecting people's lives.
However, Alan Gordon, deputy chairman of the Police Federation, which represents rank-and-file officers, said the report had allayed his fear that structural reform could damage community policing.
But he warned: "Any changes must be made for reasons of effectiveness, not financial efficiency."