Russell Myers, royal editor at the Daily Mirror, said the queen would find the documents "disturbing reading".
The chocolate biscuit cake is said to be a favourite of several members of the royal family.
Previous guests tell Yahoo UK what it is like to be at one of the Queen's Buckingham Palace garden parties.
The Queen would usually have been attending the show in London today but sent her best wishes to the virtual event.
All members of the Royal Family have been working from home as the coronavirus epidemic continues.
Though they aren't political, there are some signs that members of the monarchy, from the Queen down, are feminists.
In the new series, a romantic relationship is hinted at between the monarch and friend Lord Porchester.