Portugal has seized a trove of contemporary artwork, including paintings by Joan Miró and Piet Mondrian, from its debt-riddled owner, the government has confirmed.

For months, three Portuguese banks had tried but failed to seize the art collection from Portuguese businessman José Berardo. The 75-year-old had offered the works as collateral for his debt which totalled nearly €1bn (£920m).

The modern art collection of more than 900 works which includes, besides Miró and Mondrian, other famous artists such as Gerhard Richter and Francis Bacon, was valued in 2006 at €316m euros.

But the collection could have doubled in value since then given the growth in the art market. Bacon’s Self-Portrait, for example, sold for over €17m when it was auctioned at Sotheby’s last month.

Much of the Berardo collection has been on display to the public in Lisbon’s museums since 2006, under an agreement between the businessman and the galleries, which put them out of the banks’ reach.

It is unclear if the lenders will obtain possession of the collection, which for now remains in the state’s custody, according to Portuguese media reports.

It is not the first time Berardo’s assets have been seized. According to the media, Portugal had already taken a property of his on the island of Madeira which he had left in 1963 to make his fortune in South Africa.

Berardo had borrowed a total of €962m from the state bank Caixa Geral de Depósitos the Banco Comercial Português (BCP) and the former bank Espírito Santo, now Novo Banco. He acquired shares of BCP to become its third largest shareholder.