Police and Crime Commissioners: 'Tension' warning
The introduction of police commissioners will create "inevitable tension" with chief constables over local and national policing priorities, Sir Hugh Orde has warned.
The head of the Association of Chief Police Officers said conflict must be resolved with "mature conversations".
Reducing crime while budgets fell was another key challenge, he told the BBC.
He spoke ahead of elections in all 41 police force areas in England and Wales outside London on 15 November.
Police and Crime Commissioners (PCCs), whose duties in their area will include recruiting and dismissing chief constables, agreeing budgets and setting strategic priorities, will replace police authorities.
The Conservatives and Labour are putting up candidates in all the elections while the Liberal Democrats, while not centrally supporting candidates, have not barred members from standing. Plaid Cymru is not putting up candidates in Wales but will be supporting independents.
Sir Hugh told the BBC News Channel: "I think the inevitable tension will be about the allocation of resources to local policing and the allocation of resources to national policing.
"I would like to think most of those situations will be dealt with by mature conversations rather than overt political statements."
Sir Hugh said tension would be created by the question of "how much of a chief constable's resource can be put on local policing and how much do they have to contribute to the national policing agenda, which keeps local people safe?"
He said the introduction of PCCs represented "the biggest change to police accountability" since 1829 - the year the Metropolitan Police force was created.
"For the first time, you're seeing one person, elected locally, who will hold the chief constable to account for the delivery of policing, not just in their area but, of course, on the national policing agenda too."
The Home Office has said PCCs must "help contribute to threats which require a national policing response" - including organised crime and counter-terrorism - and work with other forces "on national policing issues through collaboration".
Sir Hugh said that, as most of those elected would be voted in "on a party ticket" it would be "far more political than anything we've seen before where 17 members of a local police authority held the chief to account".
"There's a huge variety of people standing," he added.
"Some have a great knowledge, an in-depth knowledge, of policing already - they were ex-police authority members.
"Others, less so, and we will have to make sure and work very hard with them to get them to understand the complexity of our world - this is not just about local policing."
He added: "Crime is already going down and crime continues to fall and budgets continue to fall and police and chief constables will have to deal with the increasingly difficult fiscal crisis."
On Tuesday, Home Secretary Theresa May said the success of PCCs - the brainchild of the Conservatives - would be determined by what they did in office rather than how many people voted for them.
She spoke after Labour described the elections as a "shambles" and predicted a low turnout.