A U.K. pressure group has lost its legal challenge to what it called a "sweetheart" tax deal between U.K. authorities and Goldman Sachs.

UK Uncut Legal Action, which campaigns against tax avoidance, had sought a High Court declaration that it was unlawful for the investment bank to avoid a multimillion pound interest bill on unpaid tax on bonuses.

Judge Andrew Nicol ruled Thursday that the decision was not unlawful even if it was not a "glorious episode."

The campaign group had claimed the deal cost taxpayers 20 million pounds ($31 million), though the potential cost is officially put at 8 million.

The group had claimed the deal was illegal because of requirements that all taxpayers be treated equally.

Government officials had claimed the deal had been judged "reasonable" by auditors.