Police scientists in South Yorkshire have warned they may not be able to investigate so-called "low-level" crime because of government spending cuts.
The county's forces expect budget cuts of about 25% over the next four years.
The head of South Yorkshire Police's forensic science unit said he feared his team could bear the brunt of cuts.
Kevin Morton, director of scientific support services, said: "There would be some categories of crime we just wouldn't be able to investigate."
He said that "legally and morally we are required to investigate all areas of crime".
"At the moment we have a policy of investigating all crime scientifically, but there would be some categories we wouldn't be able to that with.
"They are what we consider to be lower levels of crime.
"Obviously we would always investigate major crime, but when we are talking about criminal damage, theft of and from motor vehicles, these are crimes where we generally don't recover a lot of evidence."
Mr Morton said those crimes might no longer be considered a priority after Wednesday's Spending Review.
"The [forensic science] unit has developed over a number of years and science now is key to the frontline investigation of offences," he said.
"My main concern is if we are seen as a backroom service rather than a frontline service the possibility is that many of our services would be reduced or even removed.
"Science is one of the main investigative tools we have now within the police service."
The force's chief constable Meredydd Hughes said the effect of cuts to be announced next Wednesday would probably not be apparent to the public for two years.
"But I think you cannot impose cuts of that scale and think operational policing will not be affected," he said.
"That would be naive at best and disingenuous at worst.
"Whether it is operational uniformed police or some of the support staff, there will be noticeable changes.
"Serious funding reductions on this level are unprecedented and that brings new challenges for us as leaders of the organisation to rise to."