The panel decided that M&S could not offset losses made by its European subsidiaries against UK-earned profits.

If the High Street retailer had won, the case experts believe it had the potential to cost the Treasury hundreds of millions in tax revenue.

'Not all the relevant case law was considered and some that was considered was arguably misconstrued,' said Peter Cussons, international corporate tax partner at PricewaterhouseCoopers.

It is an opinion backed by Adam Craig, head of the EU tax group at Deloitte & Touche. 'Although (the special commissioners) consider some of the case law very thoroughly, they are very selective on the case law they examine,' he said.

Both expect M&S to appeal against the decision in the High Court, and both expect it to eventually come out on top, especially if the case gets as far as the European Court of Justice.

'We are disappointed as we strongly believe that the current UK tax legislation involved in this case is in contravention with EU law and intend to appeal to the High Court,' an M&S spokeswoman told Accountancy Age.