Public disorder will be "one of the main issues" facing British police for up to the next three years, according to former Metropolitan Police commissioner Lord Stevens.
He said it was his "gut feeling and beyond" that violence on the streets would put officers in "very difficult" situations.
Lord Stevens made the comments at the launch of an independent commission on the future of policing, which has been set up by Labour.
Shadow home secretary Yvette Cooper warned that police face a "perfect storm" of cuts in staff, "chaotic" reforms and evolving threats to the public.
She also said that morale among officers had "dropped through the floor".
"My fear is that policing now faces a perfect storm, from the scale of cuts, the chaos of confused reforms, the escalating demands on the service and declining morale.
"I'm worried in particular about the risk of a growing gap between public concerns about the need for police action but also the capacity of the police to deliver," she said.
Ms Cooper added: "The pressure on the police is growing and without further reform and action I fear that the police will not be equipped to respond.
"If we look back just over the last few months, this summer the police lost control of the streets of our major cities and the perception grew that the rule of law would not be enforced through those difficult days.
"The phone hacking scandal weakened public confidence in the relationship between the police and the press, and the latest crime figures provided the first signs that crime has stopped falling and may be starting to get worse.
"Looking forward, the pressures and challenges are inevitably growing."
She went on: "At a time when we need the police to cope, adapt, and handle more than ever before, morale has dropped through the floor."
Ms Cooper also said that Labour will field candidates for the new roles of elected police commissioners, a policy they had criticised.
The 41 commissioners, due to take office after elections next November, will replace the existing police authorities in England and Wales.
Meanwhile Lord Stevens stressed the independence of the police review, whose members include Howard Safir, former commissioner of the New YorkPolice Department.
It will look at what is expected of the police, their role in society and how to best equip them to cut crime and increase public confidence.
The commission will also consider how they are held to account, the bureaucracy that affects their work and the need to strike the right balance between the need for the police service to meet both local and national priorities.
The management of resources and the efficiencies to be found to get the most out of police spending will also be analysed.
Lord Stevens warned about the danger of public disorder returning over the coming years.
"My own belief is - and it's a very personal one - that (over) the next 18 months, two to three years, one of the main issues will be public order or rather public disorder.
"I don't think anyone would disagree with that in terms of the challenges facing policing. We'll be looking at that in some detail," he said.
The commission chairman added: "My gut feeling and beyond is that it's going to be a very difficult 18 months, two years, but I hope to God I'm wrong."
When asked to clarify if he expected disorder on the same scale as the August riots in English cities, he replied: "No, I hope not."
Policing Minister Nick Herbert has said Labour's decision to set up an inquiry was "an abdication of any kind of political leadership".
He added it was wrong for Labour to be "sub-contracting decisions on police reform, reform which they espoused in government and are now opportunistically opposing, to a committee".