A Facebook group protesting price rises since the switch to the euro has attracted more than 50,000 followers in a few months.

One of its founders, Plamen Penkov, said in a TV interview that he set up the group with friends to show extreme examples of price gaps after Bulgaria adopted the euro.

Members flag goods whose prices have jumped every day. They also share till receipts with the final totals, placed next to prices in other EU countries.

Bulgarians living abroad supply the foreign prices. According to them, a litre of fresh milk in Portugal, Spain and Greece costs about €1, while in Bulgarian shops the same amount mostly sells for between €1.70 and €1.80.

In the Italian city of Turin, restaurants sell pizzas from €5-6, and the price rarely goes above €8-9. In neighbourhood pizzerias in Bulgaria, a pizza mostly costs more than €10. Consumers in the group say these prices defy any economic logic.

Members are also building an interactive map of shops and restaurants that did not raise prices without reason when the currency changed. The map points shoppers to places with normal markups.

The organisers believe price rises can only be stopped if most people refuse to buy overpriced goods and switch to cheaper options, such as coffee made at home.