The secretive world of Italian olive oil will be laid bare after the government insisted that every bottle should show where it comes from.

Large olive oil brands, such as Filippo Berio and Bertolli, have long cultivated the image that its oil comes from rustic, rolling groves in the Italian countryside.

Instead, it often arrives in Italy in tanker trucks from destinations as diverse as Tunisia, Turkey, Greece and Spain.

According to EU laws, foreign oil can be sold as Italian olive oil if it is cut with a small amount of the domestic product.

Only four per cent of olive oil leaving Italy is pure Italian oil.

Alberto Fontana, the president of Salov, the company that makes Filippo Berio, admitted that only about a fifth of the company's oil is pressed from Italian olives.

After being blended, the oil is often said to be bottled nella tenuta, or "on the estate", despite having come from elsewhere. Last year there was a 45 per cent rise in imports of Tunisian oil.

With the law change, every bottle of Italian olive oil will have to declare which farm it comes from, and the press that extracted the oil. In the case of blended oils, a precise breakdown of the various oils will be listed.

"This will protect our star product against fraud, and make sure people know what they are getting," said Paolo De Castro, the agriculture minister.

Although Italy is famous for its olive oil, it is the second largest producer in Europe behind Spain.

Indeed, Italy cannot even produce enough oil to satisfy its domestic customers. Last year, the crop was down 13 per cent to 700,000 tonnes, while Italians used 835,000 tonnes.

Imports make up the difference, while the majority of Italy's exports are made from foreign oil. Brands such as Felippo Berio and Bertolli are not available in Italy.

The labelling will also help to erase the common practice of marking olive oil as "extra virgin".

A television investigation by RAI, the state broadcaster, tracked a load of olio di sansa, the oil that is extracted from the pulp after the extra virgin has been pressed, as it passed through Turkey.

When the oil left the Turkish port on its way to Italy, it was certified as extra virgin.