Buckingham Palace has insisted the Queen is "politically neutral" in the EU referendum campaign, following a report that she had expressed strong Eurosceptic views.
The Sun said she vented her anger with Brussels at the strongly pro-EU Nick Clegg during a lunch at Windsor Castle when he was deputy prime minister.
The former Liberal Democrat leader dismissed the report as "nonsense" while the Palace said it would not comment on "spurious, anonymously sourced claims".
The paper quoted a "senior source" as saying that people who heard their conversation "were left in no doubt at all about the Queen's views on European integration".
"It was really something, and it went on for quite a while. The EU is clearly something Her Majesty feels passionately about," the source was quoted as saying.
A Palace spokesman said: "The Queen remains politically neutral as she has for 63 years.
"We will not comment on spurious, anonymously sourced claims. The referendum is a matter for the British people to decide."
Mr Clegg wrote on his Twitter feed: "As I told the journalist this is nonsense. I've no recollection of this happening & it's not the sort of thing I would forget."
A spokesman added: "This is categorically untrue. Nick has no recollection of this conversation and it is not the sort of conversation you forget."