Police forces should merge and share resources with other emergency services or public safety will "suffer" from swingeing cost cutting, Britain's most senior policeman has warned.
All but the "core policing functions" should also be opened up to competition as forces across the country face making savings, according to Sir Bernard Hogan-Howe, the commissioner of the Metropolitan Police.
Writing in the Guardian he said that in urban areas like London police should link more closely with ambulance, fire and other services, saying there is "a bigger risk to public safety if we don't take radical action".
He wrote: "If that calls for courage, what about the structure of policing? In England and Wales there are 43 forces. The smallest has 600 officers, the largest, the Met, 32,000. They are based on 1974 local government boundaries, and in many cases emergency services are now the only county-wide services.
"Do criminals respect these county boundaries? No, they don't. They seek markets with high population densities to sell drugs and steal property. They pass local and national borders with ease. We need to be as flexible and aggressive as they are. We do not need the boundaries that currently mark out the territory of chief constables or police and crime commissioners."
Sir Bernard's intervention comes ahead of an appearance by Home Secretary Theresa May in front of the Commons' Home Affairs Committee today, where policing will be among the subjects on which she will be grilled.
Last week a police chief warned his force could be "unsustainable" within three years if funding cuts continue at current levels.
Neil Rhodes, chief constable of Lincolnshire Police, outlined his concerns in a letter to Mrs May, seen by The Daily Telegraph.
In the letter he said his force could be the first "to fall over" as cuts to officer numbers in response to a reported £10.4 million budget shortfall would mean it would be unable to police effectively.
In the Guardian, Sir Bernard pointed to Scotland, whose eight police forces were merged last year, and the Netherlands as examples of mergers that had worked, adding that changes would also allow forces to deal better with digital crime that ignores boundaries.
He said that his own force was faced with making cuts of £1.4 billion, a third of its budget, in the decade to 2020.
CCTV coverage and help for domestic abuse victims were areas where closer working among services would be a benefit as cuts bite.
He added: "Our partners face their own cost pressures, and the big concern is that if we don't work together, with a shared view of the risks, public safety will suffer."
He went on: "We have to have a shared view of the risks to public safety, from countering terrorism to child protection. We must be open about these risks with the public, politicians and the media, so we can together make informed choices about our priorities.
"We should share support services where possible, and make them as efficient as the best of the private sector. That means opening up all but core policing functions to competition.
"For example, why in London do we need three emergency services separately handling 999 calls and making similar deployments? Bring them together and it would be cheaper to run and more effective."
Asked whether David Cameron would back police force mergers, the Prime Minister's official spokesman said: "There is an issue here ... both in terms of efficiencies, but also greater co-operation between forces.
"But his view on this one hasn't changed, which is that he does believe that the structure of police forces that we have is the right approach, given the importance of retaining local accountability."
The spokesman said the PM believes there is "more that can be done" on police forces working together and sharing assets like technology and procurement services.
But he added: "In terms of going a step further and the merger of police forces, the PM's view hasn't changed."