“The Guardia Civil has arrested and investigated 21 people behind the theft of 17,500 kilogrammes of olives in the Las Vegas region,” police said, indicating 16 had been arrested and five others investigated.

In total, they robbed six farms in the Las Vegas area, a rural region that lies southeast of the Spanish capital.

The investigation began in January when a farmer complained about the theft of 8,400 kilogrammes of olives from his land, with police making the link with other similar incidents in the area involving “significant quantities of olives”.

In early February, they were alerted to the presence of five people in a vehicle carrying 140 kilogrammes of olives in broad daylight, but none of them could prove they were legally acquired.

Investigators then raided two olive presses in the Toledo and Guadalajara regions that were allegedly receiving the stolen fruit, arresting those in charge.

In total, investigators found documentation relating to the exchange of more than 17.5 tonnes of stolen olives and seized several tanks containing more than 6,000 litres of olive oil.

The detainees, aged between 20 and 57, have been charged with a variety of offences including theft, fraud and receiving stolen goods.