BERLIN - European Union regulators are unlikely to rule by the end of March on whether a UK tax scheme for multinationals breaches EU rules on state aid, Europe's competition chief said on Thursday.

The European Commission opened an investigation in October 2017 into the scheme, which exempts multinationals from UK taxes.

Diageo, London Stock Exchange, Imperial Brands, BBA Aviation, Chemring Group, Euromoney, Inchcape, Meggitt, Smith & Nephew and WPP are among the companies that have referred to the EU investigation in their accounts.

"We would prefer to take it (a decision) before Brexit would happen. I don't know whether that will happen before the end of March. Likely not," European Competition Commissioner Margrethe Vestager told reporters on the sidelines of a conference organised by the German cartel office.

Vestager has led an EU crackdown on tax avoidance, ordering Apple, Starbucks, Fiat and others to pay back taxes totalling billions of euros to various EU governments.

Vestager also said that she took Swedish music streaming service Spotify's complaint about Apple very seriously. Spotify filed a complaint this week charging Apple unfairly limits rivals to its own Apple Music streaming service.

(Reporting by Foo Yun Chee and Klaus Lauer; editing by Larry King) ((foo.yunchee@thomsonreuters.com; +32 2 287 6844; Reuters Messaging: foo.yunchee.thomsonreuters.com@reuters.net))