Police said the restaurant in Dusseldorf, western Germany, would provide the drug when customers asked for item number 40 on the menu. It is not known how much the pizzeria charged for the special order.

"That was one of the best-selling pizzas," criminal director Michael Graf von Moltke said.

The police were first tipped off by food inspectors in March, he added.

When drug squad officers began observing the restaurant, they buzzed the restaurant manager's apartment. He then proceeded to throw a bag of drugs out of the window which "fell right into the arms of the police officers", according to Dusseldorf police.

Police discovered 1.6kg of cocaine, 40g of cannabis and €268,000 (£223,480) in cash. The manager, 36, was detained for a few days.

However, he soon reopened the business and continued to sell pizza number 40 with the usual side order, police said.

That gave investigators an opportunity to look into the supply chain and after several weeks, some 150 officers busted an entire drug ring in western Germany, arresting three people, including the 22-year-old suspected head of the operation, and raided homes and businesses of another 12 suspects.

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Two cannabis farms were also discovered in nearby Mönchengladbach and Solingen, with 300 and 60 plants respectively.

The pizzeria's manager was arrested when he tried to escape the country and is still in custody.