Britain has a hung Parliament after an inconclusive result to the most tightly fought General Election in a generation.
With the votes in 36 constituencies still to be counted, David Cameron's Conservatives had secured 289 seats - making it impossible for them to reach the 326 threshold for an overall majority - setting the scene for behind-the-scenes horse-trading possibly stretching into the weekend and beyond, as the parties struggle to form a viable administration.
Gordon Brown returned to 10 Downing Street on Friday morning without any clear indication of whether he will be able to remain there as Prime Minister.
But senior lieutenants indicated that he will not "throw in the towel" until it is clear that he cannot lead an "anti-Conservative progressive majority" in the House of Commons. Lord Mandelson appeared not to rule out the possibility of Mr Brown being replaced by a new Labour leader to head a minority or coalition administration, saying: "Frankly, there are quite a number of permutations."
With 36 seats left to declare, Labour held 246 seats and the Liberal Democrats 51, indicating that the two parties are unlikely to be able to achieve an absolute majority as a coalition in the Commons unless they can also secure support from smaller parties like the Welsh and Scottish nationalists, the SDLP and the UK's first Green MP.
Mr Cameron insisted that Labour had "lost its mandate to govern", as his party raced ahead in terms of seats won in the new Parliament. The Conservatives were on target to gain more seats in this ballot than in any General Election for 80 years, said Mr Cameron after winning his Witney constituency in Oxfordshire.
But Mr Brown insisted: "My duty in all of this is that there be a stable, strong and principled government and to play my part in making that possible.
The Liberal Democrats had a disappointing night, with no sign of the so-called "Cleggmania" prompted by the historic televised leaders' debates being translated into votes or seats and their clearly deflated leader, Nick Clegg, acknowledged: "We simply didn't achieve what we hoped."
He gave no immediate indication of which party he would seek to talk to first in the wake of the inconclusive result, cautioning other leaders against "rushing into making claims or taking decisions" which did not stand the test of time.
Welsh Secretary Peter Hain made clear that Labour was ready to offer a deal on electoral reform to the Liberal Democrats in return for their support and senior Conservative frontbencher Michael Gove said Mr Cameron was "happy to talk" with other parties to ensure Britain gets a "strong and stable" Conservative-led government.