Spanish police on Monday arrested 51 people across the country -- including top members of the ruling Popular Party -- on suspicion of handing out construction permits in exchange for bribes, officials said.

They were netted in a vast probe targeting "a network of corruption" that involved local government construction contracts worth roughly 250 million euros ($315 million), the anti-corruption prosecutor's office said in a statement.

The probe was centred mainly in town halls and regional governments in Madrid and Leon in the centre of the country and Murcia and Valencia in the east.

"The collusion between local councillors and civil servants, with builders and energy service companies, and the corruption of middle-men and key companies, has helped them to secure contracts worth around 250 million euros in the last two years alone," the statement said.

Those arrested face charges of money laundering, embezzlement, and influence peddling.

The most prominent official to be detained was Francisco Granados, a former deputy president of the Madrid regional government and former senator with the conservative Popular Party which rules at the national level.

He resigned in February after daily newspaper El Mundo reported that he has 1.5 million euros in a Swiss bank account.

Members of the main opposition Socialist party were also arrested in the police raids.

The probe is the latest in a string of corruption scandals that have hit Spain's political parties, banks, football clubs and even members of the royal family.

Graft is Spaniards' second-biggest concern after the nation's sky-high unemployment rate of 24 percent, according to the latest state-sponsored poll by the Centre for Sociological Research.