Only half of police officers would definitely report a colleague who punched a suspect "a couple of times" for trying to escape arrest, an academic study into police ethics and integrity has revealed.

The Open University research found officers thought "misdemeanours" such as using excessive force on a suspect or covering up for a drink-driving colleague who caused an accident were less serious than stealing property, such as a watch or cash from a lost wallet.

The study, published amid growing public concern over police ethics after the phone-hacking scandal and the Andrew Mitchell affair, says these are not isolated examples and there is evidence of uncertainty over the boundaries between right and wrong at every level of the force.

The research, by Dr Louise Westmarland of the Open University and Professor Mike Rowe of Northumbria University, is the first national study to question a significant number of police officers about their ethics and morals.

Officers were presented with 11 possible scenarios and asked what action they would take. One scenario involved two police officers on foot patrol who surprise someone attempting to break into a car: "He runs off. They chase the suspect for about two streets before apprehending him by tackling him and wrestling him to the ground. After he is under control, both officers punch him a couple of times in the stomach as punishment for fleeing and resisting."

Asked if they thought other officers would report such behaviour, 54% said they definitely would. But 4% said they definitely would not; 6.5% said they maybe would not. A further 13% were neutral on the question, and the remaining 21% said their colleagues would "maybe" report it.

The researchers said where officers were certain that behaviour was against force policy, even in cases they thought "serious", they were often unwilling or unlikely to report it, although this varied according to area and years of service.

In the case of punching a suspect, the overwhelming majority of officers said they knew that if it was reported it would lead to the dismissal of the officer involved.

The study also found officers were often unclear about the rules covering "minor" offences such as working in their spare time or accepting free drinks and small gifts.

The research was presented at a Commons home affairs select committee seminar on police leadership and standards on Monday. The committee chairman, Keith Vaz, said: "We all expect our police officers to uphold the highest standards of integrity, but this startling research shows how, for many, the line between right and wrong is indeed blurred.

"It is also apparent that for some officers, the sense of proportion has gone wrong: use of inappropriate force and cover ups are completely unacceptable for officers of the law."

At the seminar, Sir Hugh Orde, president of the Association of Chief Police Officers (Acpo), said the Leveson inquiry had demonstrated there was no evidence of endemic corruption in British policing. "The notion that this might be a widespread problem has not been borne out," he said.

But after Hillsborough disaster and the Andrew Mitchell affair he said it was important that police were transparent and responded to public concerns about integrity. Acpo has recently reissued its guidance on second jobs, gifts and hospitality, he added.