Prime Minister Theresa May faced calls to quit on Friday after her election gamble to win a stronger mandate backfired, throwing British politics into turmoil and potentially delaying the start of Brexit negotiations. 

Below is a running total for how many seats each party holds. 

Conservative - 256

WATCH: Prime Minister May says UK 'needs a period of stability'

A possible hung parliament

"A hung parliament is the worst outcome from a markets perspective as it creates another layer of uncertainty ahead of the Brexit negotiations and chips away at what is already a short timeline to secure a deal for Britain," said Craig Erlam, an analyst with brokerage Oanda in London.

With the smaller parties more closely aligned with Labour than with the Conservatives, the prospect of Corbyn becoming prime minister no longer seems fanciful.

That would make the course of Brexit even harder to predict. During his three decades on Labour's leftist fringe, Corbyn consistently opposed European integration and denounced the EU as a corporate, capitalist body.

As party leader, Corbyn unenthusiastically campaigned for Britain to remain in the bloc, but has said that Labour would deliver Brexit if in power, albeit with very different priorities from those stated by May.

"What tonight is about is the rejection of Theresa May's version of extreme Brexit," said Keir Starmer, Labour's policy chief on Brexit, saying his party wanted to retain the benefits of the European single market and customs union.

Potential alliances

On a nerve-racking night for the Conservatives, interior minister Amber Rudd held on to her seat by a whisker, while several junior ministers were swept away. In one of many striking moments, the party lost the seat of Canterbury for the first time in a century.

If the Conservatives end up falling just short of a majority, they could potentially turn for support to Northern Ireland's Democratic Unionist Party (DUP), a natural ally, projected to win 10 seats.

But Labour had potential allies too, not least the Scottish National Party (SNP) who suffered major setbacks but still won a majority of Scottish seats.

The pro-EU, center-left Liberal Democrats were having a mixed night. Their former leader, Nick Clegg, who was deputy prime minister from 2010 to 2015, lost his seat. But former business minister Vince Cable won his back, and party leader Tim Farron held on.

If neither main party wins a clear majority, markets will have to deal with considerable uncertainty over who will form the next government and what compromises the eventual prime minister will have to make to get the support of other parties.

In 2010, when the Liberal Democrats held the balance of power, markets reacted to the uncertainty by selling sterling. This time round the choice is likely to be even less clear, with the Liberal Democrats greatly reduced in number and the pro-EU Scottish National Party likely to have more influence

The Conservatives' positioning on Brexit and, to a lesser extent other domestic issues like austerity, makes it unlikely that it could find a willing coalition partner, making a Labour-led government the most likely outcome from a hung parliament.

JP Morgan said that despite the uncertainty, that outcome could generate a rise for sterling.

"A hung parliament would in more normal circumstances be viewed as quite a negative for sterling," analyst Paul Meggyesi said in a note distributed to media on Tuesday and sent to clients at the end of last week.

"But in the post-referendum world, all political developments need to be viewed through a Brexit prism and an argument can be made that a hung parliament which delivered or held out the prospect of a softer-Brexit coalition of the left-of-center parties ... might actually be GBP positive."

UK PM May no longer able to win outright majority in parliament

British Prime Minister Theresa May can no longer win an outright majority in parliament, Reuters calculations based on partial results of the election showed.

After the results of 633 seats were declared, May's party was on 308 seats and therefore no longer able to reach the 326 mark it would need to claim a majority in Britain's 650-seat parliament.

Jeremy Corbyn, leader of the Labour Party, leaves his home on the morning after Britain's election