Copy and paste of what will happen in terms of announcement:
When Elizabeth dies, her private secretary will be the first official (i.e., not one of her relatives or part of a medical team) to convey the news. Their first act will be to contact the prime minister, where civil servants will convey the code phrase "London Bridge is down" to the prime minister using secure telephone lines.[1] The cabinet secretary and the Privy Council Office will also be informed by the private secretary.[3] The cabinet secretary will then convey the news to ministers and senior civil servants. The Foreign, Commonwealth and Development Office's Global Response Centre, based at a secret location in London, will communicate the news to the governments of the 14 other countries of which Elizabeth is queen (the Commonwealth realms), and to the governments of the other countries of the Commonwealth of Nations.[1] Government websites and social media accounts, as well as the royal family's website, will turn black, and the publication of non-urgent content must be avoided.[3]
The media would be informed by announcement to PA Media and the BBC through the Radio Alert Transmission System (RATS) and to commercial radio on the Independent Radio News through a network of blue "obit lights" which will alert presenters to play "inoffensive music" and prepare for a news flash, while BBC Two would suspend scheduled programming and switch to BBC One's broadcast of the announcement.[11] BBC News will air a pre-recorded sequence of portraits, during which the presenters on duty at the time will prepare for the formal announcement by putting on dark clothing prepared for this purpose. The Guardian has reported that The Times has 11 days of prepared coverage ready and that ITN and Sky News have long rehearsed her death, but substituting the name "Mrs Robinson".[1]