The prediction was made by the Association of Chief Police Officers (Acpo) in a confidential correspondence sent to The Guardian.
Acpo predicts the jobs of 12,000 police officers and 16,000 civilian staff will be lost as a result of spending cuts.
The Winsor review of police pay and conditions, due to be published later today will recommend cutting £180m in annual bonuses as well as overtime, according to the BBC, as the Government plans to cut its funding for the police by 20% by 2014-15.
The 43 forces in England and Wales currently employ about 244,000 people, comprising 143,000 police officers and 101,000 civilians.
An ACPO spokeswoman said: "Chief officers are determined to do all they can to drive out inefficiencies and protect frontline delivery of policing.
"Every local police force is in a different funding position and we continue to work closely with the Home Office to assess information about how they are making savings and cuttings costs.
"This is a moving picture, given the imminent announcements about potential changes to police pay and pensions. But the police service will have fewer staff in future to meet the same or greater demand, and we need to think imaginatively about delivery and incentivising staff to produce higher quality."