LONDON (Reuters) - Buckingham Palace said it had launched an official complaint with Britain’s press watchdog on Wednesday over a newspaper report that Queen Elizabeth backs a British exit from the European Union, saying the monarch remains politically neutral.

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Under the front-page headline “Queen backs Brexit”, The Sun newspaper quoted unidentified sources as saying that Elizabeth had made her opposition to British membership of the EU clear on at least two occasions over the past decade.

“The Queen remains politically neutral, as she has for 63 years,” the palace said in a statement. “We will not comment on spurious, anonymously sourced claims. The referendum is a matter for the British people to decide.”

It said aides had taken the rare step of writing to the chairman of the Independent Press Standards Organisation to complain, citing a clause of the editors’ code of conduct relating to accuracy.

Opinion polls show voters are divided over membership ahead of a June 23 referendum so even the perception that Elizabeth, who must remain above politics under Britain’s unwritten constitution, may favor an exit from the 28-member bloc could be damaging for the campaign to keep Britain in.

The Sun, owned by Rupert Murdoch’s News Corp, said the queen had told then Deputy Prime Minister Nick Clegg at a Windsor Castle lunch in 2011 that the EU was heading in the wrong direction.

Clegg called the report nonsense. “I’ve no recollection of this happening & its not the sort of thing I would forget,” he said on Twitter.

The newspaper, British’s best selling daily which has repeatedly criticized Britain’s EU membership, also said the monarch told lawmakers at a separate meeting that she did not understand Europe.

“The Sun stands by its story, which was based upon two impeccable sources and presented in a robust, accessible fashion. The Sun will defend this complaint vigorously,” a spokesman said.

Less than a week before the 2014 Scottish independence referendum, Elizabeth said she hoped Scots would think carefully about the future, a comment which was interpreted as giving support to those seeking to preserve the United Kingdom.

The queen is not the first royal to have been pulled into the increasingly febrile EU debate.

Her grandson Prince William was criticized by some papers, including the Sun, over a speech he gave to British diplomats last month about the importance of Britain working with other nations.