ECB investigating if loans made to Spanish banks contravened rules

German newspaper Die Welt am Sonntag, citing the results of its own research, said Spanish banks had borrowed funds from the ECB at a preferential interest rate of 0.5pc even though the creditworthiness of the T-bills they provide as collateral should have required them to pay 5.5pc.

The €80bn (£64bn) issue of 18 month treasury bills had been wrongly classified as carrying a top A rating when some of them were 'completely ineligible' as collateral under ECB rules, it is claimed.