POLICE chief Ken Lay is trying to ditch the popular image of police scoffing burgers on patrol.

The Chief Commissioner has written to McDonald's corporate headquarters asking it to no longer offer police discounts and freebies.

Uniformed police, ambulance officers, firefighters and the State Emergency Service can get up to half the price of meals discounted at Victoria's McDonald's outlets.

Some restaurants also offer free food or drink - a practice it is feared could lead to perceptions of bias.

Melbourne University corruption expert Professor Leslie Holmes said the move would be in line with the policies of overseas police forces that ban freebies for their officers.

He said there was also a perception that fast food restaurants offered the discounts to entice police inside as taxpayer-funded security guards.

"I suspect it is mostly harmless, but if people perceive it is wrong, then on one level it is wrong,'' Prof Holmes said.

"It is more a matter of principle rather than the cost of the free cup of coffee. It would be much cleaner if they stop offering it."

But Police Association secretary Greg Davies said the discount did no harm.

"Everyone is trying to be as pure as the driven snow these days but anyone who thinks the police force is going to act on behalf of McDonald's against some other organisation because they get a cheap hamburger from time to time is kidding themselves,'' Sen-Sgt Davies said.

Victoria police spokesman Melissa Seach said the Chief Commissioner had written to the fast food giant asking it to re-examine the policy.

"McDonald's have advised the discount is not a set policy and it was up to each outlet to decide whether the discount will be offered; therefore, there will be no change to the policy,'' Sen-Constable Seach said.

McDonald's spokesman Skye Oxenham said individual managers offered the discount in appreciation for local work done by the emergency services.

"While there is no formal policy, in many cases our company and franchised restaurants will provide uniformed police officers, ambulance officers, fire and rescue, SES and other emergency service individuals a discount on food and beverages," she said.

james.dowling2@news.com.au