Mallorcan newspaper Ultima Hora reports that the Spanish government is flying light aircraft over the country to take aerial photographs of properties where building work has been carried out and not declared. This includes additions that would increase the value of a property and therefore the amount of liable tax, such as extensions and swimming pools.

By not declaring such work, tax cheats have been able to dodge a higher Impuesto sobre Bienes Inmuebles (IBI) bill, a tax bill payable by all property owners in Spain based on the perceived value of the property in question.

The Spanish treasury’s two-year operation to trace tax cheats resulted in the collection of an extra €1.25 billion.

The highest number of fraudsters were detected in Andalusia, which includes the Costa del Sol, where inspectors found 373,224 undeclared buildings.

In Galicia, in northwestern Spain, inspectors found 213,017 secret swimming pools or extensions to villas and in Castilla y Leon, in the north of Spain, 164,141 cases were uncovered.

Aerial surveys of 28 municipalities across the Balearic Islands between 2013 and 2015, including popular tourist destinations like Mallorca and Ibiza, found 21,652 properties that had been altered in some way without being declared, reported Ultima Hora.

Treasury officials only surveyed 4,145 council areas, and found cases of fraud in 8.6 per cent of those examined.

Homeowners will have to pay an average of €60 in a one-off property tax payment as a result of the aerial inspection.

A new stage of the operation is now underway to survey 1,721 towns using satellites and 6,331 municipal areas with drones.

A spokesman for the treasury ministry said: “For each euro spent conducting this operation, we have recovered €16 which was not being paid in tax.

“We compare what has been declared to the councils and photographs of what is actually there.”