Criminals are escaping arrest because officers are having to respond to 999 calls in cars without sirens, a police union has claimed.
The West Midlands Police Federation, which represents rank and file officers on the force, said it was aware of about 100 occasions in the last year when "lights-only" Vauxhall Corsas were used.
It claimed officers were getting stuck in traffic because they are unable to use sirens to break the speed limit or run red lights.
Tom Cuddeford, the federation's deputy chairman, said in one incident police responded to reports of a colleague being assaulted but were delayed in traffic, allowing the suspect to get away.
He added that officers were "frustrated" over not having "the tools for the job".
West Midlands Police, the UK's second largest force, said its 109 siren-less Corsas were not routinely used for response duties. It has a fleet of powerful automatic transmission Vauxhall Insignia cars specifically for 999 duties.
But Mr Cuddeford said: "These are heartfelt pleas from our officers. Talking to our members, there are daily accounts of when these cars are being used with one incident or another."
Mr Cuddeford claimed the problem was down to budget cuts which meant Corsas were "being used to fill the gap".
However, the force said: "The lower specification and lower cost Corsa was chosen to enable the force to buy the higher cost Vauxhall Insignias as response vehicles."
Policing Minister Mike Penning said it was a matter for chief constables and police and crime commissioners to decide how resources were allocated within their force.
The federation has provided examples where it said officers reported delays in response times:
:: In a potential kidnap call, officers could only use blue lights and had to take their time travelling through a built-up area. One officer involved told the federation: "I hope someone can see the sense in putting sirens back on police vehicles before someone is seriously injured."
:: Officers reported being "hampered" and "frustrated" by heavy traffic while responding to a call for back-up from community support officers dealing with a shoplifter.
:: Another officer, trained as an advanced police driver, told the federation: "I find myself sat at a red light, knowing I could get through safely, but that if something went wrong I'd get kicked off (the force) for careless or reckless driving. The job is challenging enough, so please just give us the tools for the job."
West Midlands Police, which has had to make £120 million of budget cuts since 2010, is having to find further savings of £100 million over the next five years. The force has also shed 1,500 officers.
But Superintendent Kerry Blakeman, of West Midlands Police, said the Corsas were never intended for response work.
"The lower specification (and consequently lower cost) Corsa was chosen to enable the force to buy the higher cost Vauxhall Insignias as response vehicles. Previous vehicles were incurring considerable costs to the force due to continued clutch issues due to the amount of use."
Mr Blakeman added: "A blanket change of vehicles to allow neighbourhood teams to respond would mean buying a car of a generic specification, all of which would take time and more importantly money.
"Any officer can respond to an incident if they are suitably trained to drive at speed and they are in an appropriate vehicle (with lights and siren).
"Officers who are not appropriately trained and/or driving an appropriate vehicle can attend an incident as quickly and safely as possible while complying with the Road Traffic Act just as members of the public should."
Mr Penning said police reform was "working" and that rates of recorded crime in the West Midlands were down from five years ago.
He added: "It is for chief constables and police and crime commissioners to take decisions on how resources are allocated within their force.
"While we acknowledge that the police funding settlement is challenging there is no question that the police will still have the resources to do their important work."
Mr Penning said the Government had already announced plans to reform police funding "ensuring it is fair, robust and transparent".