Many of the thousands of British holidaymakers who visited the country in the past two decades returned to purchase property.
But some have fallen foul of unscrupulous developers who paid off local officers and ignored planning laws.
The Spanish government said many illegal properties could be demolished and as the first are turned to rubble, professionals have urged owners not to panic.
Alison Rolls, head of communications at Norwich and Peterborough Building Society, said: “We are monitoring these developments in Spain very closely as we are naturally concerned for our Spanish mortgage customers’ interests.
"We understand that the number of people affected so far has been tiny, but we are still treating these developments very seriously.
"The best advice to anyone thinking of buying in Spain is to use a reputable and knowledgeable local solicitor and a lender with local knowledge.”
Lino Brydges, head of overseas mortgages at NatWest International Personal Banking, added: “Home owners should not panic but those who are worried should speak to their advisers and make sure that all relevant checks were followed when their property was built or purchased to ensure all processes when obtaining their property were legal and carried out correctly.”
However, Phil James, sales adviser at Assetz International, insisted: “It’s up to the Spanish government now but it will take time for it to sort everything out.
"The properties coming under scrutiny are by the beach, are built in green zones, have more floors than the planning application or were supposed to be offices.
"However, people with legal property will see their homes increase in value. My advice is to not panic and take legal advice.”
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