A controversial role-play exam for police has left Oxfordshire with too many acting inspectors and sergeants and short of fully qualified officers.

Now Thames Valley's chief constable is leading a campaign to scrap the selection process, laid down by the Home Office, which many highly-regarded officers struggle to pass.

Peter Neyroud says the problem has reached crisis point and that it is time to declare no confidence in the exam, which many police suitable for promotion are reluctant to enter.

"This exam has got to go," he said.

"I can't run a functioning police force without qualified supervisors.

"Chief police officers have to come out occasionally and be controversial.

"The Government have got to allow chief officers, through a national framework, to promote competent officers."

Mr Neyroud warned Thames Valley would be left with a "cast of thespians" in acting roles, if the Objective Structured Performance Related Examination (OSPRE) for sergeants and inspectors was not overhauled.

Police must pass a part-one law exam and a part-two role-play test, taken at assessment centres around the country.

While most are competent at the sit-down exam paper, they have difficulty in the second part which challenges them to enact situations they would face in real-life situations as officers.

Mr Neyroud wants the role play replaced with on-the-job assessment, allowing him to promote officers after 12 months in a temporary role.

Thames Valley's head of personnel Chief Supt Paul Kirby said the force was able to fill vacancies at the moment, but too few people were passing the second part of OSPRE to meet longer-term needs.

"If this trend continues, within three years we could run out of qualified people," he said.

A Home Office spokesman said: "OSPRE is a highly effective way of testing an officer's suitability for higher rank.

"It's important there is a clear, objective, standardised way of assessing an officer's competence before promotion. OSPRE has met that need for 10 years."