The Spanish anti-corruption prosecutor is investigating Santander Bank in relation to its exposure to more than €2.3 billion (just over $3 billion) of client money with the alleged US conman Bernard Madoff, according to the Wall Street Journal.

The report said the authorities will examine the relationship between Santander, investment fund Fairfield Greenwich Group and Mr Madoff. The investigators are reportedly looking into why Santander chairman Emilio Botin dispatched his head of risk management to see Mr Madoff not long before the latter’s arrest and whether Santander officials knew of the problem.

Some investors are asserting that Fairfield Greenwich - whose clients stand to lose a reported $7.5 billion - and its executives "failed to manage properly their investments and to carry out necessary due diligence that would have uncovered the massive Ponzi scheme."