Britons with homes on the Costas are among those at risk from a £3.5 billion campaign by the environment ministry to restore and protect coastal areas from over-development.

“This is the single biggest assault on private property we have seen in the recent history of Spain,” said José Ortega, a lawyer and the head of an action group launched in Madrid to challenge the Socialist government, which is using a 20-year-old law, the Ley de Costas (Coastal Law), to clear developments along 482 miles of coastline.

Under the plan properties built within 550 yards of the beach could be confiscated by the state and in some cases demolished.

Even homes constructed entirely legally decades ago are being targeted.