With final opinion polls suggesting no political party will win a majority in Thursday's UK general election, the procedures for forming the next government have been the subject of intense discussion between three key officials dubbed the "golden triangle": Sir Jeremy Heywood, cabinet secretary, Chris Martin, the prime minister's principal private secretary, and Sir Christopher Geidt, the Queen's principal private secretary.
In a country with no written constitution, the main reference points are precedent and the Cabinet Manual, a non-binding set of guidelines drawn up by civil servants and constitutional experts in 2010.
The guiding principle is that the current prime minister, David Cameron, remains in office until he either resigns or loses a vote of confidence in parliament. The new parliament is due to assemble on May 18 for the swearing-in of new members but the first test of a new government's strength will not come until May 27, when the Queen is due to make a formal speech to parliament setting out the government's legislative programme.
If David Cameron emerges with most seats in the Commons he is expected to exercise his right as incumbent prime minister to try to put together a government - he will have several weeks to assemble the 323 votes needed for a majority.
But there could be a constitutional crunch if it became obvious that Mr Cameron could not form a majority and that the monarch was being asked to deliver a Queen's Speech that would be immediately rejected by the Commons.
The view among some Whitehall officials is that if Mr Cameron can show he has the guaranteed support of at least 315 MPs, he would be entitled to test his support in the Commons with a Queen's Speech.
Anything less than 315 and Sir Jeremy and Sir Christopher might feel obliged to ask Mr Cameron to reconsider and to let his Labour rival Ed Miliband make the first attempt at forming a government.
As the head of state, the Queen is anxious not to become dragged into the political process at a delicate moment and will rely on Sir Christopher to operate discreetly in Whitehall during the formation of the government.
The Queen has indicated she will deliver her speech to parliament even if there is still a doubt over whether the prospective prime minister will be able to command a majority when the Commons votes on the plans a week later in early June.
With such an uncertain election aftermath in prospect, senior civil servants are gearing up for weeks of instability as they prepare to support party leaders through potentially protracted negotiations.
Discreet locations around Westminster where the party leaders and their teams can meet to haggle over terms for a coalition beyond the reach of prying media eyes have been identified. Arrangements have been made to keep negotiators fed and watered through long days and nights.
Key to all that happens in the wake of an inconclusive election result will be Sir Jeremy, cabinet secretary. Having served both Labour and Conservative prime ministers, he is regarded as the most influential and trusted public servant of his generation.
Insiders say Sir Jeremy's overriding objectives are ensuring that the Queen remains above political controversy and that nothing occurs to sully the civil service's reputation for impartiality.
In pursuit of the former goal he will be in frequent contact with Sir Christopher, an urbane former public schoolboy who passed through Sandhurst before being commissioned as an officer in the army Intelligence Corps and then joining the Foreign Office.
Chris Martin, a former Treasury official who is principal private secretary to the prime minister, makes up the third member of the "golden triangle" of officials.
The process of arriving at a coalition deal may well take longer this time than it did five years ago as the party leaders come under far greater pressure from their MPs and rank and file members to explain how a tie-up will benefit them.
Akash Paun, who has studied minority governments for the Institute for Government, a Whitehall-watching think-tank, said: "The parties might well want to tie down the other party to more detail than in 2010."
In an appearance before a parliamentary committee earlier this year, Sir Jeremy set clear limits on the role he would be prepared to see the civil service play.
Whitehall "would be very happy to supply information on the cost of something or the legislative requirements of something or the timetable required to do something".
It would not, however, supply policy advice, for fear that "you are effectively being asked to provide advice against policies as well as in favour of them". Whitehall's position could then "be caricatured as favouring one party or one coalition over another, and that would not be the right place for the civil service", he told MPs.
Despite some initial qualms, Whitehall adapted well to the challenge of coalition government, but some old hands believe the prospect that no party will be able to form a majority government will force a second, and far more testing, shift in the way the civil service works.
One former mandarin said Whitehall was working on the assumption that "a minority government where each vote has to be negotiated" was at least as probable as another coalition.
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