If you let your property to tourists, you are probably in breach of the law. Second-home owners are warned to be on their guard as tourism and tax authorities in Spain are clamping down on unregistered lets. Those who advertise their properties on the web for holiday lets face fines of up to 30,000 euros if caught.

Legally, these apartments and villas should be registered with the tourism authorities, but conditions are extremely stringent. In practice, hardly any privately-owned properties are licensed for holiday rentals. In addition to fines for illegal holiday letting, owners of these properties could face the wrath of both the Spanish tax authorities and, if they are expatriates, those in their home country, if rental earnings are not declared.

More than 300,000 expatriate property investors in Spain are British. With recent interest rate rises and the slowing down of the housing market, more and more are turning to the tourism market to offset their losses.

Given the fact that buy-to-let mortgages are more readily available nowadays, many expatriates have been seduced into investing in property in Spain with rental income from holidaymakers paying their mortgage and providing them with an additional income. An average two-bedroom apartment with a sea view can net as much as 1,400 euros per week in the height of the summer season.

A number of Brits with property in the Balearic Islands and on the Andalucía coast have revealed that they were reported to the authorities by their Spanish neighbours for letting out their premises. Most say they bought their second homes for investment purposes and that, after advertising them on the Internet for holiday rental, were booked solid for most of the year.

However, they now face five-figure fines, in some cases considerably more than they have earned from letting the property – which was, in most instances, merely a way of paying the mortgage. Most have no idea the premises require licensing from the tourist authorities to be used as holiday rentals until they are hit with legal action.