Members of the Royal family are rushing to Balmoral to be by the Queen's side following a health update from Buckingham Palace.
A Palace spokesperson said: "Following further evaluation this morning, the Queen's doctors are concerned for Her Majesty's health and have recommended she remain under medical supervision. The Queen remains comfortable and at Balmoral."
Many of people, including MP's, the Prime Minister, Scotland's First Minister and First Minister of Wales have offered their sentiments to Her Majesty. While the Royal officials state the Queen is comfortable, there is a question of what lies in store for a mourning United Kingdom, whenever she may pass.
READ MORE- Queen under medical supervision at Balmoral as doctors 'concerned for her health'
Plans are reported to be in place for national protocols that will be enacted in the event of the death of the Queen - a plan known as Operation London Bridge, reports Examiner Live.
However, if she passes in Balmoral in Aberdeenshire, Operation Unicorn will be put in place. Here is the 10-day plan regarding what will happen if the Queen dies.
Operation Unicorn
In the circumstances of the Queen’s death, parliamentary business at Holyrood and Westminster will be suspended immediately so the authorities can prepare for her state funeral.
It is also expected for thousands of people to venture to Scotland - with the Scottish Parliament, Holyrood and St Giles’ Cathedral identified as focal points for members of the public who wish to pay their respects.
The Queen's body will be moved from Balmoral down to Holyroodhouse in Edinburgh.
Then it will be carried up the Royal Mile to St Giles for a funeral service before being transported by the Royal Train which will take her back to London down the east coast mainline for the burial service.
Keep up with the latest updates with our live blog here.
Day one
When Her Majesty passes away, the Prime Minister, Liz Truss, will be one of the first people to be informed by by Queen’s Private Secretary and sent to members of the Privy Council Office.
MPs and senior civil servants will receive a call and an email stating: "Dear colleagues, It is with sadness that I write to inform you of the death of Her Majesty The Queen."
This will sit in tandem with an announcement on social media and flags are to be at half-mast within 10 minutes of the news.
We can also expect the soon-to-be crowned King Charles will address the nation in a televised broadcast. If he's in London, the Prime Minister will hold an audience with Charles. Meanwhile the Ministry of Defence will organise gun salutes and a minute of silence will be held across the country.
Day two
According to POLITICO reports, Prince Charles will be named the new king and a proclamation will be read out at St James' Palace and the Royal Exchange. In the House of Commons, MPs will also give tributes after the PM's statement the day before.
Her Majesty's coffin will return to Buckingham Palace. If she has passed away in Scotland, St Giles church in Edinburgh will provide a funeral service before her body is transported by the Royal Train back to London.
Days three-four
Once the Queen's body and family return to London, King Charles III will set off on his UK tour, visiting the Scottish Parliament and St Giles Cathedral in Edinburgh, then Northern Ireland's Hillsborough Castle and a service at St Anne's Cathedral, Belfast.
Meanwhile in London, rehearsals for the funeral will be taking place.
Day five
Five days later, a procession will begin, starting at Buckingham Palace and ending at the Houses of Parliament, before the service will at Westminster Hall.
The Queen will then lie in state for three days, as members of the public visit to see her coffin.
Days 6-9
King Charles will visit the Welsh Parliament and service at Cardiff's Liandaff Cathedral.
During these final days, The Government will be finalising their plans for the day of the funeral, as hundreds of thousands of mourners flock to the streets.
Day 10: The Queen's funeral
Although it will be a Day of National Mourning, employers will not be obligated to give staff a day off. A two minute silence held across Britain.
The funeral will take place at Westminster Abbey, followed by a committal service at St George's Chapel, Windsor Castle, where Queen Elizabeth II will be buried the King George IV Memorial Chapel.
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