Image copyright PA Image caption Nick Clegg called the Sun's story "nonsense"

Buckingham Palace has complained to the press watchdog over the Sun newspaper's article claiming the Queen backed "Brexit" from the European Union.

The Sun quotes anonymous sources, one of whom claims to have witnessed a "bust-up" between the Queen and pro-EU former Deputy PM Nick Clegg in 2011.

The palace insisted the Queen was "politically neutral" while Mr Clegg called the story "nonsense".

But the Sun said it stood by its story and would defend itself "vigorously".

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Under the headline, "Queen backs Brexit", the Sun said the Queen's exchange with Mr Clegg at a lunch in 2011 left "no room for doubt about her passionate feelings over Europe".

It said her "reprimand" of Mr Clegg "went on for some time and stunned other guests".

The paper says the Queen also revealed her feelings about Europe during a separate conversation with MPs at Buckingham Palace "a few years ago".

It claims the Queen told them: "I don't understand Europe" - words an unnamed parliamentary source says she spoke with "venom and emotion".

Following the complaint the newspaper said: "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."

Analysis

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By Peter Hunt, BBC Royal correspondent

It is unusual for the Queen to take action against a newspaper.

It is a sign of the depth of regal displeasure.

It is the Sun headline, "Queen Backs Brexit" which is both toxic and very troubling to an institution which prides itself on remaining above the political fray.

But the course of action the palace has now embarked upon brings with it risks. It's a far cry from the "never complain, never explain" mantra once deployed by officials in the past.

The letter to the press watchdog ensures that the Sun story continues to be debated.

And there continues to be a focus on what the Queen chose very deliberately to do four days before the Scottish referendum.

When she told a well-wisher in 2014 "I hope people will think very carefully about the future", it was interpreted as support for Scotland remaining within the UK.

It was a planned remark the Queen and her senior advisers may come to regret.

Read more from Peter

A Buckingham Palace spokesman said: "We can confirm that we have this morning written to the chairman of the Independent Press Standards Organisation to register a complaint about the front page story in today's Sun newspaper.

"The complaint relates to Clause One of the Editors' Code of Practice."

The Editors' Code of Practice is regulated by the Independent Press Standards Organisation (IPSO). Clause One refers to accuracy, saying "the Press must take care not to publish inaccurate, misleading or distorted information or images, including headlines not supported by the text".

It also states "while free to editorialise and campaign, the Press must distinguish clearly between comment, conjecture and fact".

'Politically impartial'

The Sun's political editor Tom Newton Dunn wrote that the paper would not have reported the Queen's remarks "had they not come from two different and impeccably placed sources".

He says the Queen must remain "above the fray" of political issues, but added: "If she has a view on Brexit, don't voters have a right to know what it is?"

Professor Vernon Bogdanor, constitutional expert at Kings College London, told the Press Association it was "absurd" that the Queen would break from her tradition of political impartiality after decades as monarch.

"I'm very dubious. The Queen speaks and acts on the advice of ministers," Prof Bogdanor said. "What she said on the Scottish referendum was that people should think carefully before they vote - and that's a very sensible comment, I would have thought."