McDonald's has come up with a secret trick to help stop drunks fighting while they line up for a late-night Big Mac.

McDonald's is looking for more civilised diners who don't want to have a carpark brawl, and is attempting to calm customers so they don't have the urge to fight people who may have pushed in line or spilled their coke.

The chain trialled playing classical music over its speakers during the late hours to see if it affected the way drunk diners behaved - and it worked.

Glasgow, Scotland, was the first city to try the classical music trick and Stockport, England, tested it two years ago when violence at the restaurant was rife.

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Diners at McDonald's restaurants in Gloucester and Liverpool, in the UK, can now scoff down chips and burgers while listening to the tunes of Bach and Mozart.

A McDonald's Australia spokeswoman told news.com.au playing classical music in restaurants was not company policy, but individual restaurants had done it in the past.

A McDonald's New Zealand spokesman said this morning that from time-to-time the restaurants have to deal with anti-social behaviour - like any business that operates late at night.

"In general the most effective solution we've found is to have security on at peak times, late night. Staff get extensive training, which includes dealing with difficult customers, and there are protocols in place to ensure staff and customers are safe. We're always looking at new ways to address anti-social behaviour, and consider different approaches

Last year, a drunken brawl at an Adelaide McDonald's restaurant led to jail time for one of the men involved and a video went viral in 2015 showing young men spraying security guards with fire extinguishers at a restaurant in Newcastle, about 160km from Sydney.

An insider at the McDonald's restaurant on King St told the Newcastle Herald there were growing concerns about late night violence at the fast food outlet.

The source claimed staff feared for their safety as drunk and drug-affected diners turned on them. Some of the out-of-control behaviour included fights, barging past the counter to help themselves to food and vandalism.

A McDonald's UK spokesperson told the Mirror: "We have tested the effects of classical music in the past and played it in some of our restaurants as it encourages more acceptable behaviour.

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"Typically, classical music is played from early evening onwards and, in some cases, on certain nights in a small number of restaurants."

Duke University's Dr Kevin Laber found classical music calmed people as it released pleasure-inducing dopamine and repressed the release of stress hormones.

Music has been used in the past to try and change the behaviour of Australians.

In 2006, former Rockdale mayor Bill Saravinovski blared Barry Manilow and Doris Day through speakers to discourage hoons from hanging out in carparks.

That plan however did not work for the council so local politicians settled for a heavier police presence.