As exit polls predicted the Conservative Party is to be largest party in a hung parliament. Labour cannot now win a majority, but it is not clear which party will be in a position to form a government.
The counting process begins amidst reports of angry scenes at some polling stations where people were still queuing to vote past the 10pm deadline.
There were reports of queues in Sheffield, Leeds, Newcastle and other parts of the country.
Houghton and Sunderland South has won the race to become the first constituency to declare a result.
The constituency declared at 2252 BST. Labour's Bridget Phillipson won the seat with 19,137 votes.
The first Northern Ireland results have been declared. In north Antrim, the DUP's Ian Paisley Jnr polled 19,672 votes, winning the seat comfortably.
DUP leader Peter Robinson speaking after he lost his seat of 31 years to the Alliance Party's Naomi Long said he would have 'preferred not to stand' as a candidate in East Belfast.
Gordon and Sarah Brown arrived in a flurry of flashbulbs at the count in Kirkcaldy. He held onto his seat with an increased majority of nearly 5,000 votes.
Conservative Party leader David Cameron enjoyed a drink in a pub on the way to the count in his Witney constituency.
After winning his seat with an increased majority, Mr Cameron said it was clear from the results announced that the country wanted "change" and that would require "new leadership".
Liberal Democrat leader Nick Clegg has apologised to voters who have been waiting in long queues at a polling station in his Sheffield constituency. Police were called to move people who staged sit-in protests at three polling stations in the city.
Former home secretary Jacqui Smith lost her Redditch seat. Speaking after her defeat she said it's been "an immense honour" to have served and "I'm obviously sad that's come to an end tonight".
The Green Party's Caroline Lucas wins Brighton Pavilion, becoming the party's first Westminster MP. She says the people of the constituency have made history. "Thank you so much for putting the politics of hope above the politics of fear."
Conservative party workers watch TV coverage of the results as the sun rises on Friday morning. It is likely to be some hours before it is clear who is in the best position to form the next British government.
In the morning it became clear that the Conservatives have won the most MPs in the UK general election but fallen short of a majority, leading to the first hung parliament since 1974.
Arriving back at Lib Dem headquarters in London, Nick CLegg said: "It is vital that all parties, all political leaders, act in the national interest and not out of narrow party political advantage", adding the Tories had the first right to seek to govern.
Standing outside number 10 Gordon Brown said he "respects" the right of the Lib Dems to talk to the Tories about forming a government. But he said he was still PM and, if talks failed, would open negotiations with the Lib Dems.
David Cameron reached out to the Liberal Democrats in an effort to form a government. The Tory leader said he wanted to make a "big open and comprehensive offer" to the Lib Dems.