More than 1,100 civil servants have been working unpaid round-the-clock shifts for more than a week to prepare for the Queen's funeral tomorrow.
A core team of around 100 officials are staffing a central operational response team co-ordinated by the Cabinet Office tasked with delivering the biggest public service operation since the Olympics - and one of the largest ever in the UK - with virtually no notice.
Staff turned up to work on Thursday last week and did not leave until the following day as the news they most dreaded came through from Balmoral.
As word of the monarch's passing broke, hundreds - including nearly every current civil servant who had been involved in planning Operation London Bridge over several years - immediately put themselves forward to help.
A daily ministerial meeting is chaired by Nadhim Zahawi in his role as Chancellor of the Duchy of Lancaster, with the National Situation Centre constantly providing updated information to cabinet members.
More than 400 Foreign Commonwealth and Development Office (FCDO) volunteers are helping co-ordinate the massive challenge of receiving 500 dignitaries around the world with just 10 days' notice - the equivalent of hundreds of state visits in less than two weeks.
Additionally the Department of Culture Media and Sport (DCMS) has dispatched around 300 civil service martials to support the Queen's lying-in-state - with duties including handing out tissues for those overcome by emotion.
The volunteers are among "thousands" of staff across all parts of the civil service working three shift patterns supporting the massive effort to make Monday run smoothly.
Insiders say that although TVs will be playing in Whitehall on Monday, the hectic nature of the task means they will not be able to watch coverage of the day until it is all over.
Bosses say it's too early to confirm the cost to the civil service of co-ordinating the Queen's funeral.y
But sources maintain that the transition to a new government led by Liz Truss hasn't been affected by the massive civil service effort, and that departments will not be depleted when they return to business as usual on Tuesday.
Liz Truss is to have an audience with King Charles III before attending his reception for visiting heads of state at Buckingham Palace.
The King and Queen Consort will host world leaders and official overseas guests at the palace, in what the King's spokesman described as an "official state event".
The Prime Minister will also meet Irish Taoiseach Micheal Martin, Canadian prime minister Justin Trudeau and Polish president Andrzej Duda in Downing Street.
It comes as world leaders travel to the UK ahead of Monday's funeral service.
The DCMS has said the historic occasion will be shown on giant screens in various locations across the UK - from London's Hyde Park to Coleraine Town Hall in Northern Ireland.
