La Caixa, Spain's largest savings bank, has become embroiled in a political funding scandal that could affect its plans to create a national energy champion from its stakes in several Spanish utilities.

Barcelona-based La Caixa last year forgave almost €7m ($8.2m, £4.8m) in overdue interest on a loan to the Catalan Socialist party, without explaining why the party was singled out for preferential treatment, according to Spain's Tribunal of Accounts, which audits political party finances.