While the advocate general's comments are not binding, judges follow them in most cases. The ruling could cause conflict as British Prime Minister Theresa May has vowed to make the legal changes necessary to stop the European court from delivering legally binding judgements on the country which is set to leave the EU in 2019.
In a case brought by the English Bridge Union, the advocate general said bridge was a sport because it required mental effort as part of a challenge, noting that European Union law had no definition of sport beyond excluding games of chance.
EU law requires proof of benefits to physical or mental well being for a sport to claim VAT exemption. To insist that only physical activity was required would exclude recognised sports such as shooting and archery, the adviser said.
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Britain's tax collectors, HM Revenue and Customs, had refused to reimburse the English Bridge Union for VAT payments on entry fees to tournaments.
So-called duplicate bridge is considered a sport by the tax authorities of Austria, Denmark, France, the Netherlands, and Belgium, but not by Ireland and Sweden.
Played by four individuals in two teams, in clubs, tournaments, and online, it was classified as a sport by the International Olympic Committee in 1998.
Last year, the European Court of Justice faced criticism from Britons who campaigned to leave the European Union before the June 2016 referendum, with the official "Vote Leave" group saying Britain lost most of its cases to the court.
However, the court has backed London on cases involving challenges to British welfare rules and has upheld sanctions on Russia also challenged by Moscow that Britain strongly supports.
(Reporting by Elizabeth Miles, editing by Pritha Sarkar)
