The forum says resources have been focused on community policing
A serious shortage in the number of detectives is being made worse by increased investment in community policing, it has been claimed.
The National Detectives Forum, a specialist unit which advises the Police Federation, says there is a shortfall of 5,000 detectives.
It fears the crisis means the standard to become a detective has dropped.
It adds that the creation of the Serious Organised Crimes Agency also diminishes regional detectives' roles.
The forum says the problem has been partly caused by an increased emphasis on neighbourhood policing and the diversion of resources into hiring more community support officers.
There is such an acute crisis in the recruitment of detectives in England and Wales, the forum adds, that over the past two decades the pass mark of those wanting to join CID departments has been lowered from 80% to 48.6%.
Dennis Weeks from the Metropolitan Police runs the Detectives Forum. He says numbers have to be kept up.
"There'll always be some villains getting away with it, that's the nature of the beast, but to catch the optimum amount there needs to be a good investment in detective officers, in police officers.
"The level of investigation, the degree of evidence that is required, the nuances of that evidence that need to be met, have all increased, and I don't think that police numbers have increased with that pace."
The Association of Chief Police Officers said improving career structures is the answer, not cutting back on community policing.
A spokesman said: "We share federation concerns about attracting good quality officers into the CID and undoubtedly issues around remunerations, work life balance and how the specialism is regarded within the service are part of that equation.
"Work is continuing at national level to address this challenge but the solution is not to detract from neighbourhood Policing or to undervalue the contribution made by our PCSOs."
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