Crime and policing are major battlegrounds in the election, as Conservative claims of "broken Britain" are contrasted with Labour claims of increased police numbers, reduced crime and a robust policy on terrorism. Since I left the Metropolitan Police in 2008, I have called for acknowledgement by all political parties that there are grave policing issues to be addressed. Almost 50 years since the last royal commission on the subject, it is time to approach policing in Britain in a holistic and cross-party manner.

This is not going to happen before the election, if at all. In the meantime, I suspect we may soon discover, when all the manifestos have been scrutinised, that those charged with writing the sections on crime within them will have cast their eyes admiringly across the Atlantic. In November 2008, a man named Chuck Wexler gave a speech on comparisons between American and British policing. He is a frequent visitor to Britain, but his expertise lies in having been chief executive of the Police Executive

Research Forum in Washington, DC, the nearest body in the US to the Association of Chief Police Officers here. The audience was a mixture of police chiefs, police authority members and politicians with home affairs briefs from different national parties. Wexler has been involved in policing for most of his life and holds an honorary MBE for services to police co-operation across the Atlantic. His message was unequivocal: the British police were better organised, trained and led than their American counterparts, and the mechanisms for holding them to political account were incomparably better. Dominic Grieve, the then Tory shadow home secretary, was reported to be very irritated to have been invited to hear such views.

I would hazard a guess that any shadow home team would have been both irritated and surprised because, for the past 15 years or so, it has been a mantra among politicians of almost all stripes here in Britain that US policing is muscular, democratically accountable and effective. I beg to disagree: Wexler is right.

There are some good things about American policing - there are some good police forces and federal agencies, including the FBI, and some very fine officers - but much police work in the US is characterised by chronic underfunding, political interference, chaotic boundaries, non-existent managerial training and poor standards. Wexler knows this well, because his organisation, a voluntary association of police chiefs who have more than 100 officers under their command, has been struggling for years to do something about it.

But in this, US policing reflects America itself, particularly the divide between federal and state activity, and the contrast between the big cities, with their celebrated forces, such as the New York, Los Angeles and Chicago Police Departments, and most of the rest of the country. There are 17,000 separate forces, often with a handful of officers. Martha's Vineyard, for instance - playground of the rich, holiday destination of the Obamas and smaller than the Isle of Wight - has six, which may explain something about Chappaquiddick. The division between local forces, state troopers, sheriffs and the FBI (aka "famous but ineffective", according to local officers) has to be seen to be believed.

There are more than 50 federal law-enforcement agencies, including the Bureau of Alcohol, Tobacco, Firearms and Explosives, which organised events at Waco, losing officers in the process before handing over to the FBI, with even more catastrophic results. After 11 September, the department of homeland security was created; it seems unfortunate that this remains separate from its equivalent in both the FBI and the CIA.

Intelligence-sharing is virtually impossible, most agencies are unable to afford to exploit ­advances in DNA and other technologies, and a co-ordinated response to emergencies requires creating expensive "fusion centres" to bring agencies together. The 2002 case of the Washington sniper is a case in point. The investigation was led by a very small force, with others coming on board as more incidents occurred in the many jurisdictions around Washington. There is no equivalent of HM Inspectorate of Constabulary or a Home Office to enforce standards.

So what is it about the US that has attracted home secretaries from Michael Howard to David Blunkett and Jack Straw, as well as the likes of Dominic Grieve? Three things: localness, simplicity of accountability and apparent success, mostly, but not only, in New York.

The Americans have got localness right. On Martha's Vineyard, the largest department is in Edgartown; it consists of about 25 officers. These are mostly local men and women, and their chief is visible and accountable. They are not interested in much that happens elsewhere, in cross-border crime or in counterterrorism, which are all matters for someone else. Their citizens are satisfied and proud of their local police. In this, Britain has much to envy.

Politicians admire the simplicity of accoun­tability in America. Police chiefs are political appointments, coming and going with, or at the behest of, the mayor. I was the 24th commissioner of the Met; the NYPD and the LAPD, founded decades later, have had 41 and 54 chiefs respectively, not necessarily a successful formula for leading enormous organisations. No reason needs to be given for dismissing a chief; Sarah Palin allegedly sacked her police chief in Anchorage, Alaska, for his refusal to fire a junior officer embroiled in a messy divorce with her sister. And many people think that Bill Bratton, the most effective commissioner of New York City, was fired by Rudy Giuliani for having the temerity to appear on the front cover of Time magazine as the man who had saved New York from crime; Mayor Giuliani thought the accolade should be his. (Giuliani later made Bernard Kerik New York's top cop, after he had served a very short career on the front line; Kerik is now serving time in a federal penitentiary.)

Our politicians have also been mesmerised by the turnaround in crime in New York but have not been prepared to analyse properly what lay behind it. First of all, the numbers: at its height, the NYPD had 41,000 officers; in London the figure has never risen above 32,000, to police a city with a similar population but twice the geographic size, and carrying out functions that, in New York, are shared with the FBI, the Secret Service and the Drug Enforcement Administration. Second, the costs seemed attractive: the NYPD's budget appeared to be much smaller than that of the Met - until the Met itself, stung by the comparison, discovered that the costs of NYPD buildings, vehicles, technology and pensions are covered by the budget of the city of New York. Third, the scale of the reduction in crime seemed astonishing, until one realised how terrible the problem had become. Bratton used to illustrate this with an apocryphal anecdote of his first morning, when he asked a cop how long it would take to walk to the headquarters from his apartment block. "No idea," came the reply. "No one has ever got that far."

Bratton inherited a force that had been very lightly managed; with the support of the chattering classes, he drove down crime by changing that dramatically. But it came at a price. A dreadful death in custody was dismissed by a mayoral aide as "collateral damage". The much-vaunted "zero tolerance" was, in effect, "targeted intolerance" and pretty ugly. Crime is down, New York is safer, but its murder rate is still more than three times that of London.

Pick and choose

As Britain approaches an election, much of this background has been forgotten as the parties have picked and chosen aspects of US policing to include in their manifestos. The Tories, for instance, struck by the apparent straightforwardness of accountability in America, in contrast to the complexity and general invisibility of police authorities here, want to introduce directly elected "commissioners" to recruit and dismiss police chiefs as Palin and Giuliani could. They are right to highlight a problem with accountability; the solution just happens to be wrong, because it threatens the most important aspect of British policing. It took 150 years to develop operational independence - it should not be replaced with political acquiescence.

Labour, meanwhile, is toying with introducing neighbourhood referendums about crime problems; these would be binding on local police. Yet the slide from democracy through populism into vigilantism might be tricky, particularly in a ward that elects the BNP.

I am certain there are many things about British policing that can be changed for the better. Some of those ideas may come from the US. It would not be difficult to improve local accountability here, for instance, by introducing compulsory mechanisms for consultation using new technology. The Americans have also been clever enough not to muck about with their statistics, with the result that when crime rises or falls, their public believes in it. By contrast, the Tories' home affairs spokesman, Chris Grayling, has found out that no proper comparison of crime levels is possible in Britain because we have changed the basis for collecting data too often. But if he becomes home secretary, he will also find this does not matter, because no one believes the statistics any more.

I am not being complacent about policing in Britain. Policing is a profession that deals in disasters, some of their own making, in Britain

as in the US. That is unlikely to change. My concern, however, is that focusing on America won't fix the malaise in British policing. Unless our politicians let go of their fixation with officer numbers and allow the service to use far more auxiliary and ­support staff to free officers to get out of police stations, policing as a public service will become unaffordable. We need to recognise sooner rather than later the problems of living with a fraying accountability structure designed in 1964, when the police had neither radios nor ­internet, when international terrorism played no part in domestic life, when we had a citizenry schooled in the obedience of war.

These should be matters of cross-party concern, of equal weight to decisions about who wins and who loses between the three armed services. It seems odd to have a strategic defence review without having something similar for the police. But perhaps too many politicians have been watching The Wire.

Ian Blair was head of the Metropolitan Police from 2005-2008