The Sun newspaper's editor has denied any wrongdoing after the UK press regulator ruled that his paper mislead its readers by claiming that The Queen backed breaking away from the EU in a front-page story.

The Independent Press Standards Organisation (IPSO) said the popular tabloid's "Queen backs Brexit" headline in March was "was not supported by the text and was significantly misleading. The headline contained a serious and unsupported allegation that the Queen had fundamentally breached her constitutional obligations in the context of a vitally important national debate."

The Sun, 8 March edition
The Sun's 8 March 2016 front page Neil Henderson/Twitter

The Rupert Murdoch-owned daily has published the ruling in Wednesday's edition (18 May), while editor Tony Gallagher took to the airwaves to defend the headline and story, which did not breach the Editor's Code of Practice.

"I don't accept we made an error at all. We made a judgement that the headline was right and backed up by the story," Gallagher told BBC Radio 4's Today programme.

"We knew more than we put in the public domain, the sources were so impeccable that we had no choice but to run the story in the way that we did."

The story claimed the monarch had a "bust-up" with ex-deputy prime minister Nick Clegg in 2011 at Windsor Castle over Europe and that she was critical of the EU at a reception for MPs at Buckingham Palace.

Clegg called the story "nonsense" after its publication while Buckingham Palace complained about the article, stressing that The Queen was always politically neutral. Gallagher added: "Nick Clegg had a number of opportunities to deny the story before it went to print and he didn't do so.

"He only denied the story after it created a furore and after having some consultation with the palace."

Justice Secretary and Brexit backer Michael Gove was forced to deny he was a source for the story after it emerged he attended the Windsor Castle meeting.

"We don't comment on private conversations with the Queen," a spokesperson for the cabinet minister said at the time.