A highly detailed plan is in place to break the news to the nation when the Queen dies.

A special codeword will be used as well as a detailed procedure for the following hours and days with everything from her undertaker's name to the number of pall bearers and the length of gunfire salute in her honour.

Her senior doctor, gastroenterologist Professor Huw Thomas, is likely to oversee her last hours and it is he who will control access to her room and help decide what information should be made public.

According to a report when she dies it will be Sir Christopher Geidt, the Queen’s private secretary, who will spread the news, first contacting the prime minister, the Mirror Online said .

Queen Elizabeth II and Prince Philip, Duke of Edinburgh process down the Mall during Trooping the Colour (Photo by Chris Jackson/Getty Images)

The Queen will be known by the codeword “London Bridge" and civil servants will say “London Bridge is down” on secure lines.

From the Foreign Office’s Global Response Centre in London the news will go out to the 15 governments outside the UK where the Queen is also the head of state, and the 36 other nations of the Commonwealth for whom she has served as a symbolic figurehead.

The public will find out in a newsflash after newspapers and television and radio stations have been told.

At Buckingham Palace a footman will pin a black-edged notice to the gates and the palace website will be transformed into a sombre, single page, showing the same text.

At commercial radio stations a blue "Obit light" will glow to tell DJs to play appropriate music and go to news at the next available moment.

BBC One, Two and Four will be interrupted and revert to their respective idents – an exercise class in a village hall, a swan waiting on a pond- and then the news will come on.

Listeners to Radio 4 and Radio 5 live will hear the specific formulation of words, “This is the BBC from London."

London Bridge is down is the code word that will be used when the Queen dies

Both houses of parliament will be recalled, people will go home from work early, and aircraft pilots will announce the news to their passengers.

The Prince of Wales will become king and Camilla the queen and will visit, England, Wales, Scotland and Northern Ireland.

If the Queen dies abroad, a BAe 146 jet from the RAF’s No 32 squadron, known as the Royal Flight, will take off from Northolt , with a coffin from royal undertakers, Leverton & Sons.

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Footage from the day Diana's body flown into RAF Northolt

If she dies in Scotland her body will lie at rest at Holyrood house, in Edinburgh, where she is traditionally guarded by the Royal Company of Archers, who wear eagle feathers in their bonnets.

Her body will be transported by train to London.

A 41-gun salute – almost seven minutes of artillery – will be fired from Hyde Park

In every scenario, the Queen’s body returns to the throne room in Buckingham Palace where there will be an altar, the pall, the royal standard, and four Grenadier Guards, their bearskin hats inclined, their rifles pointing to the floor, standing watch.

Everything has been being planned since the 1960s and will swing into action with precision.

If the Queen dies during Royal Ascot , the meet will be scrapped while The Marylebone Cricket Club is said to hold insurance for a similar outcome if she passes away during a home test match at Lord’s.

The National Theatre will close if the news breaks before 4pm, and stay open if not.

All games, including golf, will be banned in the Royal Parks, and many sporting fixtures will be cancelled.

Everything has been being planned since the 1960s and will swing into action with precision

The day after her death flags flying at half mast will be raised and Charles will be proclaimed king and trumpeters from the Life Guards, wearing red plumes on their helmets, will step on the roof of Buckingham Palace and give three blasts.

A 41-gun salute – almost seven minutes of artillery – will be fired from Hyde Park.

There will be a huge funeral 10 days later and int he meantime the Queen's coffin will move to Westminster Hall, to lie in state for four full days - around half a million people are expected to visit.

There will be ten pall bearers who will practice their role in secret - British royals are buried in lead-lined coffins and Princess Diana’s weighed a quarter of a ton.

Four soldiers will stand silent vigil for 20 minutes at a time, with two ready in reserve.

The wreaths will be changed every day.

The funeral will have 2,000 guests and there will be a procession before the Queen's body is taken by road to Windsor Castle where she will be buried in the royal vault.

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