Luxembourg has pledged to overhaul its culture of financial secrecy, as it fought back against the latest accusations that it helped leading multinationals avoid billions of dollars of tax.

The claims could prove highly embarrassing to Jean-Claude Juncker, the new president of the European Commission, who was prime minister when the corporate tax deals were allegedly struck.

Officials were responding to a report that more than 340 multinationals, including such names as Pepsi, Procter & Gamble and JPMorgan, made secret deals with the Grand Duchy between 2002 and 2010 that saved them billions in taxes. The commission is already investigating whether rulings agreed by the Luxembourg tax authority with Fiat Finance and Trade, the financial arm of the car company, and Amazon, the internet retailer, amounted to state aid.