West Midlands Police and Crime Commissioner David Jamieson says he is concerned that crime in the region could soar as a result of "dysfunctional" police forces in West Mercia and Warwickshire.
An alliance between those two forces was due to end last week after West Mercia decided to pull out.
But the split was delayed for six months by Home Secretary Priti Patel, who warned there would be a "severe" impact on Warwickshire if the alliance ended without agreed terms.
Mr Jamieson said West Midlands Police had been working with the Warwickshire force to avert any threat to public safety caused by the split.
Speaking at a meeting of the West Midlands Strategic Policing board, he criticised the way West Mercia had handled the situation and warned about the potential impact on the West Midlands Police area.
"I am concerned that dysfunctional police forces at West Midlands Police’s borders may have an impact on crime here too," he said.
"Open warfare between Warwickshire and West Mercia Police does no-one any favours, there are no winners here, apart from the criminals."
The crime rate has shot up in the West Midlands Police force area in recent years, with violent crime, burglary and robbery all hitting record levels.
Mr Jamieson warned that the fall out from the split could lead to "expensive legal action" as Warwickshire attempts to re-coup lost funds from the divorce.
"We are already stepping-in to support Warwickshire Police with their IT and will be looking at other ways of ensuring they remain a viable police force," he added.
"The arrangements will be on a contractual basis and I am very clear that whatever support they receive will not be at the detriment of the West Midlands.
"It also has to be said that the manner that West Mercia Police’s PCC and Chief Constable have acted is very concerning.
"They’ve pulled out of an alliance that was delivering savings and protecting officer numbers."
West Mercia Police and Crime Commissioner John Campion said: “Mr Jamieson oversees a policing area with some of the worst problems in the country around violence, knife crime, serious organised crime, drugs, burglary and robbery.
"That’s in spite of the fact that he receives around £60 more per head of population in central police funding than we do in West Mercia.”
“With that in mind, it’s perhaps no surprise he is trying to deflect attention away from his own inept, dysfunctional performance. He would be better served thinking about how he continues to fail his police force and his communities, rather than wading into subjects where he has no knowledge and even less credibility.”