If Theresa May does not resign, but the party decide to make a challenge on her leadership, the following steps will need to be taken:

• 15% of elected MPs will need to write a letter to the chairman of the 1922 Committee of backbenchers (Graham Brady) saying they have no confidence in the leader
• If the forecast of 318 seats is fulfilled, Graham Brady would need to receive 48 letters (it would be 48 letters for any final tally from 315-320)
• At that point, all MPs then vote on a no confidence motion.

If a motion of no confidence is carried through, the Conservative Party would then follow the steps for a normal leadership contest:

• Each leadership candidate would need to get a proposer and a seconder for their nomination
• They then go through a series of rounds where the MP with the lowest number of MP nominations is eliminated until two candidates are left
• Those two candidates then go to the party on a One Member, One Vote basis

• However, if there is only one candidate when nominations close, that member will be declared leader of the party.

Key wins for Labour over the Conservatives in Wales on general election night

Election 2017

Senior Labour MP Yvette Cooper says "it's great we're winning back seats for Labour" and "I applaud the hard work of Jeremy Corbyn and all activists."

Theresa May called this election as "a referendum on herself and she has lost, I don't see how she can carry on", she adds.

Ms Cooper voted against Jeremy Corbyn in last year's leadership election, but now stresses "he won twice and that's why the party came together in this campaign to achieve this result".

Professor John Curtice
Polling expert

It has been a mixed result for the Lib Dems. They have so far gained 8 seats and lost 3, including former leader Nick Clegg's Sheffield seat.

The party has on average seen a small increase in its support in constituencies with the largest number of those with degrees, and indeed in London, but otherwise has typically fallen back.

However, there have been a number of notable personal performances such as gains in Bath, Eastbourne, and Twickenham.

Election 2017

Conservative Stephen Crabb says he thinks Theresa May can stay, adding: "There is a duty on her to form a viable government."

The Haverfordwest MP, who backed the Remain campaign in the EU referendum, says: "Theresa May clearly understands the seriousness of the situation."

He says "something has gone awry here... and we're emerging with a situation of more divisions and less stability".

Labour's Alan Whitehead has held Southampton Test, with an increased majority - which means there will be a hung Parliament.

Election 2017

Theresa May's mood was "calm" and "sombre" when she addressed staff at Conservative Party HQ - but she "didn't directly refer to her future", BBC political editor Laura Kuenssberg says.

She didn't say she would stay, and the fact she didn't mention this could mean she hasn't made up her mind yet, and "puts the chance of resignation on the table", Laura adds.

630 seats declared, 20 to go. The Conservatives currently have 306 seats and are short of a majority by 20 seats.

They have, therefore, to win all that remain to avoid a hung Parliament.

Chris Johnston
Business reporter, BBC News

Kathleen Brooks, at City Index, says the pound has remained relatively stable, suggesting that the prospect of a hung Parliament and even a second election is not triggering market panic.