The national ministry of finance has uncovered 21,652 properties in the Balearics that have been hidden from the treasury. Using aerial photography, it has scanned 28 municipalities in pursuing a plan linked to a war on fraud that was launched in 2013.

The relevant town halls have, therefore, been informed about these properties, for which no property tax payments had been received. The ministry maintains that this is not a campaign against illegal building but against tax fraud from construction that has not been declared with the town halls. "It is about locating property that uses municipal public services at the cost of owners who have fully declared their properties," says a ministry spokesperson.

The type of fraud varies. Some 35%, a total of 7.578, corresponds to renovations and changes of use that have not been declared. A further 25% - 5,413 - are cases where there have been extensions, while 29% (6,279) are new buildings. The remaining 2,382 are swimming-pools that have not been declared.

The detection of all these properties has had a benefit for town halls because the average value of the properties has increased and has led to an average rise of 309 euros of property tax. The 28 town halls have, therefore, received more than six million euros all told. The 2013 plan is to continue into next year, and so the municipalities that have yet to be covered will have the opportunity to be so.

When the plan was launched in 2013, the finance minister, Cristobal Montoro, said that the state had an obligation to tackle this type of fraud. He explained that if a chalet is built on an urban plot without being declared, it has the same services for lighting, sewage, water and rubbish collection as properties that are declared. Once an illegal property is found, the ministry lets the relevant town hall know. It then includes it on the municipal register to ensure that owners meet their tax obligations.

This plan doesn't penalise illegal works as such. These are the responsibility of the town halls and island councils.