The chief constable of West Mercia retired after his request to stay on for a further year was refused, it has emerged.
Paul West has run the force for eight years but was told his extension request could not be considered.
He will retire in the summer following 32 years' service.
"West Mercia Police needed a chief constable in post on a longer-term basis," said Sheila Blagg, chair of West Mercia Police Authority.
Hire and fire
The chief constable will leave before the first police commissioner is elected in May 2012.
The Police Reform and Social Responsibility Bill, which allows for elected commissioners, is currently going through Parliament.
If approved, commissioners will replace 41 police authorities to manage police budgets, set local priorities and hire and fire chief constables.
Paul West's retirement means the incoming commissioner could not easily appoint a top policeman of his own choosing, as there will already be a chief constable in place.
Ms Blagg added: "The force is facing some major long-term challenges, which includes the introduction of police commissioners."
A new chief constable is expected to be in the post by July.