If you're keeping track, MI5 is the UK Security Service. That's not to be confused with MI6, of course, which is the Secret Intelligence Service, which works to protect UK interests abroad. (The fictional James Bond "works" for the latter in Ian Fleming's novels and the film series.)
While at the MI5 headquarters, the Queen met with Sir Parker... Andrew Parker, the agency's Director General, and also took a look at its museum. She was also given a private intelligence briefing while there. The details of that aren't known, because they were for her eyes only.
Her Majesty gave a very special speech while at MI5, in which she thanked intelligence officers for their services to the country.
"There will no doubt continue to be significant threats and challenges ahead," she said. "But on each of my visits to MI5, I have been impressed by the way that you have adapted to the changing threats to our nation.
"Because of the nature of your work, it is without public recognition, so it is on behalf of the country that I say to you all, thank you."
‘I am always struck by the remarkable resolve with which you carry out your vital role.’
Watch The Queen’s MI5 speech in full. pic.twitter.com/cDY56dtj4R
— The Royal Family (@RoyalFamily) February 25, 2020
While touring the MI5 museum, Her Majesty learned about how MI5 used disinformation to win the Second World War and confuse the Nazis. A double agent known only as "Garbo" – who has since been recognized as the late Juan Pujol – created a fake group of informants that tricked Nazi High Command by giving them the wrong date and location of the D-Day landings.
According to the Jersey Evening Post, the monarch also heard about how her late father, King George VI, played a part in MI5's disinformation campaign during World War II by making a visit to an "oil depot" in Dover intended to raise spirits across the UK. In reality, the depot had been built by a film studio. Clever!
For years, the Queen herself was rumoured to have had a role in this campaign, but she wasn't letting any secrets slip, according to the Telegraph. The Jersey Evening Post reports that Andrew called the disinformation campaign "the most important thing MI5 has done," and the monarch replied calmly, neither shaken or stirred, "And very successfully, too."