The Government could launch an inquiry into how national plans to honour the memory of the Queen after her death were leaked.
The detailed arrangements known by the codename London Bridge – which cover everything from the lowering of flags to an address by the Prince of Wales – were published by the Politico website on Friday.
Information about Operation Spring Tide – the plan for Charles’ accession to the throne – was also published.
It included extraordinary details from confidential memos, which revealed fears that London could become "full" for the first time as millions flock to the capital to pay their respects.
The Daily Telegraph quoted a senior Government source as saying the Cabinet Office had started an investigation into the leak.
“If it turns out to be an old version that was widely circulated and does not include the most sensitive material, it might go no further than that – but if it’s a fuller version that is only circulated to, say, 10 people, then the Cabinet Office will launch a formal inquiry,” the source said.
Buckingham Palace declined to comment.
But Palace officials were outraged over the leak of the sensitive and deeply intimate information, according to the Mirror.
A royal source told the paper: “It is deeply disturbing that such private information which is not only deeply personal to the Queen but also has widespread security implications has been revealed.”
This day will be known by officials as “D-Day” and a series of events are planned on each successive day up until “D-Day+10” when the Queen’s state funeral will be held at Westminster Abbey.
The leak comes just ahead of the Prime Minister’s first visit to Balmoral since 2019, according to reports.
Boris Johnson and wife Carrie are said to have received an invitation from the Queen to stay at her Scottish home this weekend.