The Conservative Party, led by Prime Minister David Cameron, won an unexpected majority victory of ten seats; they had been leading a coalition government with the Liberal Democrats.

The opposition Labour Party, led by Ed Miliband, saw a small increase in its share of the vote to 30.4 per cent, but it won 26 fewer seats than in 2010, giving them 232 MPs.

The Liberal Democrats, junior coalition partners led by Deputy Prime Minister Nick Clegg, suffered heavy losses, losing 49 of their 57 seats.

The Green Party of England and Wales won its highest ever vote share of 3.8 per cent, and their only MP, Caroline Lucas, retained her seat, Brighton Pavilion.

All British, Irish, and Commonwealth citizens over the age of 18 and residing in the UK who were not in prison or a mental hospital or a fugitive on the date of the election were permitted to vote.

[12][13] The Government increased the amount of money that parties and candidates were allowed to spend on campaigning during the election by 23%, a move decided against the advice of the Electoral Commission.

No sovereign had refused a request for dissolution since the beginning of the 20th century, and the practice had evolved that a prime minister would typically call a general election to be held at a tactically convenient time within the final two years of a Parliament's lifespan, to maximise the chance of an electoral victory for their party.

[18] However, the prime minister had the power, by order made by Statutory Instrument under section 1(5) of the Fixed-term Parliaments Act 2011, to fix the polling day to be up to two months later than 7 May 2015.

[22] Alongside Brown and Hague, 17 former cabinet ministers stood down at the election, including Stephen Dorrell, Jack Straw, Alistair Darling, David Blunkett, Sir Malcolm Rifkind and Dame Tessa Jowell.

[25][26] In order to emphasise this, The Economist stated that "the familiar three-party system of the Tories, Labour, and the Lib Dems appears to be breaking down with the rise of UKIP, the Greens and the SNP."

In the run-up to the election, David Cameron coined the phrase "Carlisle principle" for the idea that checks and balances are required to ensure that devolution to Scotland has no adverse effects on other parts of the United Kingdom.

[70][71] The phrase references a fear that Carlisle, being the English town closest to the Scottish border, could be affected economically by preferential tax rates in Scotland.

[74][75] This was also associated with a rise in multi-party politics, with increased support for UKIP, the SNP and the Greens.Britain faces a simple and inescapable choice – stability and strong Government with me, or chaos with Ed Miliband: https://facebook.com/DavidCameronOfficial/posts/979082725449379 The question of what the different parties would do in the likely event of an inconclusive result dominated much of the campaign.

Smaller parties focused on the power this would bring them in negotiations; Labour and the Conservatives both insisted that they were working towards winning overall majorities, while they were also reported to be preparing for the possibility of a second election later in the year.

[110] Additionally, issues were raised about the continued existence of the BBC, as the DUP, UKIP and Conservatives had made a number of statements criticising the institution,[111] and support for same-sex marriage.

[114][115][72] Each would also make it a condition of any agreement with Labour that Trident nuclear weapons were not replaced; the Green Party of England and Wales stated that "austerity is a red line".

[127] During the campaign, TV news coverage was dominated by horse race journalism, focusing on the how close Labour and the Conservatives were according to the polls, and speculation on possible coalition outcomes.

[129] Similarly, Steve Barnett, Professor of Communications at the University of Westminster, said that, while partisanship has always been part of British newspaper campaigning, in this election it was "more relentless and more one-sided" in favour of the Conservatives and against Labour and the other parties.

[132] Print media was hostile towards Labour at levels "not seen since the 1992 general election",[131][135][138][139] when Neil Kinnock was "attacked hard and hit below the belt repeatedly".

[132] The Daily Mail ran a headline suggesting SNP leader Nicola Sturgeon was "the most dangerous woman in Britain"[131][141] and, at other times, called her a "glamorous power-dressing imperatrix" and said that she "would make Hillary Clinton look human".

[131][133] The five most prominent politicians were David Cameron (Con) (15% of TV and press appearances), Ed Miliband (Lab) (14.7%), Nick Clegg (Lib Dem) (6.5%), Nicola Sturgeon (SNP) (5.7%), and Nigel Farage (UKIP) (5.5%).

[146] Labour's lead gradually declined throughout 2014, largely attributed to increases in support for the SNP and the Green Party, as the Conservatives remained relatively level.

[148] The final polls showed a mixture of small Conservative and Labour leads and ties with both between 31 and 36%, UKIP on 11–16%, the Lib Dems on 8–10%, the Greens on 4–6%, and the SNP on 4–5% of the national vote.

as of 7 May 2015 as of 7 May 2015 as of 7 May 2015 as of 7 May 2015 (New Statesman)as of 7 May 2015 as of 7 May 2015[174] as of 7 May 2015 as of 7 May 2015 An exit poll, collected by Ipsos MORI and GfK on behalf of the BBC, ITN and Sky News, was published at 10 pm at the end of voting.

"[234] Re-elected Green Party MP Caroline Lucas agreed, saying: "The political system in this country is broken [...] It's ever clearer tonight that the time for electoral reform is long overdue, and it's only proportional representation that will deliver a Parliament that is truly legitimate and better reflects the people it is meant to represent.

On 9 December, an Election Court decided that although he had told a "blatant lie" in a TV interview, it had not been proven beyond reasonable doubt that he had committed an "illegal practice" under the Representation of the People Act[244] and he was allowed to retain his seat.

[249][246] The higher fine for the Conservatives reflected both the extent of the wrongdoing (which extended to the 2014 parliamentary by-elections in Clacton, Newark and Rochester and Strood) and 'the unreasonable uncooperative conduct by the Party'.

[251] At constituency level, related alleged breaches of spending regulations led to 'unprecedented'[249] police investigations for possible criminal conduct of between 20 and 30 Conservative Party MPs.

"[252] On 2 June 2017, charges were brought under the Representation of the People Act 1983 against Craig Mackinlay, who was elected Conservative MP for South Thanet in 2015, his agent Nathan Gray, and a party activist, Marion Little.

[258][259][260] It also found that UKIP MEPs had unlawfully spent EU money on other assistance for national campaigning purposes during 2014–16 and docked their salaries to recoup the mis-spent funds.