The editor in chief of the Sun has said the public will "have to have to take my word" that the newspaper's story alleging the Queen "backs Brexit" is accurate, amid mounting speculation over who leaked an alleged conversation between the monarch and Nick Clegg.
Buckingham Palace complained to the press watchdog on Wednesday after the tabloid splashed on a leaked 2011 conversation in which she reportedly lambasted the direction of "European integration" to the then deputy prime minister.
Labour has written Cabinet Secretary Sir Jeremy Heywood demanding an inquiry into who leaked the Queen's remarks.
As the rest of the press sought the paper's source - suggesting Justice Secretary Michael Gove, who also attended the lunch - editor Tony Gallagher said his team was "completely confident" it was accurate and said the paper "knew more than we published".
He denied the paper had overwritten its headline, which suggested the Queen's five-year-old remarks amounted to her wanting Britain to leave the EU in the June referendum.
"We knew much more than we published and that remains the case," he told the Today programme on Thursday. "Two sources came to us with information about the Queen and her views on the EU. We would've been derelict in our duty of us to not put that in the paper.
"It's as simple as that. The fact the story is inconvenient for a number of people is not my fault. We serve our readers, not the elite."
Presenter Mishal Husain probed him on the headline, arguing the story, which claimed the Queen had said the EU was "heading in the wrong direction", did not support it.
She pointed out that the palace complaint to the Independent Press Standards Organisation (Ipso) is under Clause One of its code that prohibits headlines "not supported by the text".
Gallagher said: "You're going to have to take my word for it that we're completely confident the Queen's views were expressed exactly as we've outlined in both the headline and the story.
"It is also the case that we knew much more than we published and that remains the case. We are in no doubt that the story is accurate."
He also said there was a "second occasion", as well as the 2011 lunch attended by Clegg, where the Queen had made "similarly scathing remarks".
Husain pushed Gallagher over whether the Queen's alleged comments, said well before an EU referendum was even announced, could have amounted to her backing Brexit.
Gallagher said this was "semantics" but Husain insisted it was "entirely different". "There are plenty of people who were disparaging five years ago who are backing for the UK to stay in the EU," she said. Gallagher replied that the state of the eurozone and the European Union in 2011 suggested someone with Eurosceptic views then, would back a Brexit now.
Gallagher would not give details of the second incident where the Queen was said to have made anti-EU claims, saying it would trigger an "absurd mole hunt" among the rest of the press.
Today's papers have named Gove, who is backing a Brexit, as one of the Sun's possible sources.
The Daily Telegraph reported Gove, who was Education Secretary at the time, had "refused to deny" it.
On Today, Gallagher told Hussein: "You wouldn't expect for a single moment to reveal anything about the sourcing of a story... Those of a cynical mind might think there's an attempt to take Michael Gove out of the Leave campaign."
Clegg has denied he was the source and said he cannot remember the conversation. He said: "I've no recollection of this happening and its not the sort of thing I would forget."
The Sun's political editor, Tom Newton Dunn, who wrote the piece, called this a "non denial denial," a term used by journalists to describe an attack on a story that does not actually refute its assertions.
Labour MP Wes Streeting has written to the cabinet secretary asking for an inquiry. "Let's see what comes back," a party spokesman said.
Chris Grayling, Leader of The House of Commons, said private conversations with The Queen "should always be kept private".
But Grayling, who is Lord President of the Council, the head of the Privy Council, the role Clegg was fulfilling at the time of his alleged meeting, stopped short of calling for an official investigation into the leak, and instead said the press watchdog was right to look into the story.
David Cameron has also ruled out an inquiry.
He told BBC Sussex: "The Palace has made a very clear statement, the former deputy prime minister has made a very clear statement saying that this didn't happen and I think we should leave it at that.
"There is obviously a proper investigation now being held by the press complaints commission and I think we should let them do their work."