Senior officers should be barred from standing as police and crime commissioners for a "cooling-off" period of four years after leaving their force, MPs reviewing some of the most radical reforms to policing in 50 years said today.
The restriction would help avoid any conflicts of interests where holders of the controversial new role were scrutinising decisions they made while still in office, the MPs said.
The Commons Home Affairs Select Committee also warned there was a need for the concept of operational responsibility to be clarified, with police - not politicians - being "solely responsible for individual decisions with respect to arrest and investigation".
They added that, while police and crime commissioners could help hand power back to the public, this was not inevitable and would depend both on the job description set by Government and who takes up these roles.
"The concern would be that if police and crime commissioners could not cope with the workload, or could not successfully represent the entire force area, the public's opportunities to engage with the police might get worse rather than better," they said.
The committee recommended that police and crime commissioners are given a support team to help them cope with the expected increase in letters and emails from the public, "otherwise there is a risk that public engagement will turn to public disillusionment".
The controversial move to replace existing police authorities and put locally-elected police and crime commissioners in charge of multimillion-pound force budgets with the power to sack chief constables was announced by Home Secretary Theresa May in July.
The committee said there should be no restrictions on who can stand for the role when the first elections are held in May 2012.
But it suggested a cooling-off period of four years - the equivalent of one term for a police and crime commissioner - for a former officer, ranked as assistant chief constable or above, who wants to stand in the same area in which he or she has served.
Keith Vaz, the committee's chairman, said the move was "to ensure that there is not the slightest hint of a conflict of interest between a former chief constable and the area he or she policed".
The report added that the issues of operational independence, operational responsibility and the role and powers of police and crime panels all "need further attention".
Mr Vaz said: "We recommend a policing charter which will define clearly and precisely where the writ of the commissioner ends and the responsibility of the chief constable begins.
"In abolishing police authorities and introducing directly-elected police and crime commissioners, the Government is placing a huge responsibility on these individuals.
"They will have a high volume of work and large geographical areas to cover. They will need effective teams of support staff, and the advice of strong police and crime panels if they are to do their jobs well."
The new commissioners should be responsible for the budget, staff, estate and other assets in their force area, and have the same power to appoint and dismiss senior police officers which is currently held by police authorities, the committee said.
It added that members of police and crime panels, which will be introduced in a "robust overview role", should mainly be councillors in the force area with appropriate responsibilities.
And there should be a political balance on the panels, with a smaller number of independent members.
The committee also recommended that it would be a better use of public money if these panels were used as a means of providing advice for the commissioners before final decisions are made, as opposed to setting them up as a separate scrutiny body examining decisions after they have already been taken.
Vernon Coaker, Labour's shadow policing minister, said: "A single elected police chief for an area as large as the West Midlands, Greater Manchester or Devon and Cornwall will do little to improve police accountability, but will risk politicising the police and at a huge cost to the public.
"At a time when police funding is being slashed by 20%, people will not understand why the Government wants to spend an estimated £100 million - the equivalent of 600 full-time officers - on this controversial top-down experiment. The Government should think again."
Rob Garnham, chairman of the Association of Police Authorities (APA), warned that the introduction of police and crime commissioners created "the very real risk of politicising police accountability through single-issue elections".
He echoed the committee's concerns over the workload and large geographical areas that will need to be covered by the new commissioners.
"At present 17 members, including nine elected councillors and eight independent members of the community, share the work of holding the force to account and managing finances," he said.
"A single individual would need a significant number of support staff to enable him or her to be as effective as the current model.
"This would essentially mean employing staff to carry out the work that police authority members do now, but at a much greater cost."
Mr Garnham went on: "In the interests of local people, the APA calls again for HMIC to undertake an impact assessment of the proposal, so that all consequences of this proposed new model of accountability can be independently examined."
Richard Kemp, vice-chairman of the Local Government Association (LGA), said: "If the police are to be truly held accountable at local level, then councils must be at the heart of any new system.
"It is reassuring the Home Affairs Select Committee shares this view, as well as LGA concerns about directly-elected police commissioners."
But Police and Criminal Justice Minister Nick Herbert said the new commissioners "will replace weak and invisible police authorities".
They will help to give the public "a greater say over how their community is policed, making forces truly accountable to the communities they serve, and ensuring that the police are crime fighters and not form writers," he said.
"The operational independence of chief constables will be protected."
Chief Constable Mark Rowley, of the Association of Chief Police Officers (Acpo), said: "The police service expects robust accountability in everything that we do.
"The Government has been emphatic in its commitment to operational independence, which alongside local accountability is a cornerstone of British policing.
"We are very clear that it is not for chief constables to determine the way in which we should be held to account for the quality of policing we provide to local communities. But we do have a right to clarity about how the arrangements are intended to work."