The question of just how long it should take to eat fast food is being answered by the burger giant McDonald's, which is making customers finish within 45 minutes or face a charge of £125.

Motorists who care to linger over their McMeals for any longer at some drive-throughs are receiving demands from a private company that manages car parks for the burger chain.

If they do not pay, the fee rises steadily and customers are threatened with court action and approached by bailiffs. A spokeswoman for McDonald's said the 45-minute restrictions had been introduced at about 40 restaurants because car parks were being abused. She said signs explaining the policy were displayed and leaflets given out.

Many supermarkets and restaurants are handing over the management of their car parks to companies which use number plate recognition cameras to log when people enter and leave.

If they stay too long, the details of the registered keeper of the vehicle are obtained from the Driver and Vehicle Licensing Agency (DVLA), and he or she is billed. An elderly Wiltshire couple were recently berated by Tesco after taking too long to do their Christmas shopping at the supermarket.

The company that manages McDonald's car parks, Civil Enforcement, also works with a string of other blue-chip companies. BP used it until recently to monitor some of its petrol station forecourts.

One motorist, Jamie Thomson, told the Guardian of his experience at a McDonald's near Gatwick: "I ordered a burger, chips, a doughnut, coke and coffee. I sat in my car eating my lunch, and listening to the radio. After eating, I continued to sip my coffee for a time, and ate my doughnut. Then I left. All perfectly normal." He says he was in his car for about an hour.

Several weeks later, he received a letter from Civil Enforcement demanding £125, or £75 if the charge was paid quickly. At first Thomson, a businessman from Sussex, did not even realise that he was being charged for spending too long at McDonald's, as the notice gave only a partial address.

When he remembered his visit to McDonald's, Thomson asked Civil Enforcement for photographic proof of his "offence", but was told he would have to pay for a photo. He contacted the DVLA to ask how Civil Enforcement had obtained his details, and was told the DVLA releases data to bodies which have "reasonable cause" to ask for it.

McDonald's told Thomson that the use of "enforcement methods" happened only in "extreme" circumstances. The company added: "At this restaurant we have stipulated that a member of the public may be parked for 45 minutes unless permission is given to stay longer by the duty manager."

McDonald's in effect washed its hands of the charge, saying it had been imposed by Civil Enforcement and the burger giant did not profit from it.

Thomson's charge has risen to £213. He has been threatened with court action and received a letter from a debt collection company. He said that neither he nor any member of his family would eat at the chain again.

Civil Enforcement operates more than 700 car parks, and says it issues a "considerable number" of parking tickets every year. Its founder, Gary Wayne, argued its "hi-tech approach" was "less confrontational than clamping and towing".