An estimated one million Britons live most or all of the year in Spain, where they are thought to own more than 100,000 second homes. They have collectively invested billions of pounds in areas that had been virtually abandoned in previous decades.

Critics say that previously unspoilt areas have been changed for good because of unchecked construction. Greenpeace says that the equivalent of three football pitches of land on the Spanish coastline is disappearing under concrete every day.

Many British homeowners on the Spanish coast have had their building permits declared illegal after corruption scandals in town halls throughout Spain.

The entire city government of Marbella, on the Costa del Sol, was sacked in 2006 after a corruption scam was uncovered by police.

About 30,000 homes have been built there illegally in the past ten years. At least 4,500 of them, many owned by expatriates, face court decisions on whether they should be demolished.

The Socialist Government is also vowing to clear Spanish beaches of illegal dwellings. The new plan could result in further demolitions in areas such as the Mediterranean coast from Barcelona in the north to Marbella in the south, the Canary Islands and the Balearic Islands.

Properties in Tenerife, Málaga and Gran Canaria, as well as Almeria, are also under threat. Thousands of Britons who bought homes costing an average of £200,000 in the village of Catral, near Alicante, have been warned that they could be demolished.

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