AS BRITAIN enters its final day of campaigning before its most unpredictable election in a generation, none of the major parties are on track to command a parliamentary majority, meaning the May 7 vote could have a messy outcome.

Here are the leaders of the main factions vying for a slice of Westminister:

The incumbent - Conservative Party leader David Cameron

Prime Minister David Cameron's career hangs by a thread, whether he wins or loses this knife-edge election, his career hangs by a thread.

If he loses, it's over instantly. And even if he wins but doesn't secure an overall majority, he could face a leadership challenge from inside his famously ruthless party.

Mr Cameron came to power in a coalition with the centre-left Liberal Democrats in 2010, and wants a European Union membership referendum, which he hopes will cure his country and party of its Eurosceptic angst.

While polls show voters generally like him personally, Mr Cameron, 48, is the product of an unusually privileged background. A descendant of King William IV and the son of a wealthy stockbroker, he attended the exclusive Eton College and Oxford University, and married a woman who traces her ancestry back to another king - Charles II of England.

His strongest boast is that he pulled the economy from a deep downturn to deliver one of the fastest growth rates in the developed world. But real wage growth has only just started to pick up, meaning many voters say the recovery hasn't benefited them.

Mr Cameron tried to change the party's reputation for being indifferent to the poor and intolerant of gays and ethnic minorities. He legalised gay marriage, increased foreign aid and appointed Britain's first female Muslim Cabinet member.

But this was set back by his approach to the Budget deficit, pushing through cuts to welfare spending, which the opposition Labour Party said forced the most vulnerable to pay to clean up a mess made by rich bankers.

The geek - Labour Party leader Ed Miliband

If Labour leader Ed Miliband is to win power, he must convince millions of voters that "Red Ed", a self-confessed socialist geek, can be trusted to lead the world's fifth-largest economy.

Mr Miliband, 45, has already shed some of his social awkwardness and pitched a resilient, more human face, even laughing at some of his own imperfections.

Cast by opponents as a dangerous London socialist out of touch with the real world, he is gambling that British politics has atomised, crumbling the middle ground and opening up space for less gleaming politicians.

His tough past year included a speech at the Labour conference where he forgot to mention the deficit and a failed plot to oust him as leader.

During his battle to win the leadership of the Labour Party in 2010, some opponents cast him as Forrest Gump, the simpleton film hero played by Tom Hanks, who unwittingly pops up at key moments in US history. Opponents would continue to seize on Mr Miliband's looks and mannerisms, comparing him to TV's hapless oddball Mr Bean.

The son of a prominent Marxist academic father and a campaigning activist mother, Mr Miliband grew up in a highly politicised household, attended an ordinary North London school, but went on to read Philosophy, Politics and Economics at Oxford University. He is married to environmental lawyer Justine Thornton, and they have two young sons.

Mr Miliband's has promised higher top tax rates and fewer tax loopholes for the rich, and price caps on energy utilities and property rentals.

The promise-breaker - Liberal Democrat leader Nick Clegg

Deputy Prime Minister Nick Clegg is fighting to retain his seat in Parliament and save his political career.

Support for his centrist Liberal Democrats, or "Lib Dems", has plummeted since the party won almost one in four votes in the 2010 General Election. That put them in government for the first time since 1945 as the Conservatives' junior coalition partner.

But now about a third of the Lib Dem's 57 seats across Britain now under threat.

Traditionally Britain's third party, the Liberal Democrats were accused of selling out by forming the coalition.

But the act that most heavily damaged Mr Clegg's reputation was breaking a pledge not to raise university tuition fees, made before the last election.

Mr Clegg was elected to the European Parliament as a Liberal Democrat in 1999, became a British MP in 2005, and became leader of the party two years later. He says he wants to remain the Liberal Democrat leader "in all circumstances" after this election.

Born in Buckinghamshire in south-east England to a Dutch mother and a half-Russian father, Mr Clegg, 48, speaks English, Dutch, French, Spanish and German. He studied at the University of Cambridge as well as in the United States and Belgium, and has three sons with his wife, Spanish lawyer Miriam Gonzalez Durantez.

He began his career in journalism in Hungary in 1993 before taking up a European Commission post and later becoming an adviser to then Conservative trade commissioner Leon Brittan.

The 'man of the people' - UKIP leader Nigel Farage

Mr Nigel Farage has turned the United Kingdom Independence Party (UKIP) into a national force but is also battling for his future, with some commentators saying he has run out of steam.

He was expected to triumph in the televised leaders' debates, but failed to shine. He has admitted struggling at the start of the campaign, blaming back pain from a 2010 plane crash.

Rarely photographed without a pint of beer, the charismatic 51-year-old has said he will quit the party leadership "within 10 minutes" if he does not win the seat he is contesting.

Anti-EU and anti-political correctness, the plain-speaking and populist Mr Farage reminds UKIP's base of older, white, blue-collar voters of a bygone era when the economy felt stronger, immigration was lower and Britain was great.

He was born in 1964 to an affluent family in Kent, south-east England. His father was a stockbroker - and an alcoholic - and his parents divorced when he was five. He was educated at top private school in London. Rather than attending university, he followed his father into the City of London as a commodities trader.

He joined UKIP in 1993 as a founder member and was elected to the European Parliament in 1999. He led the UKIP to top the polls in last year's European Parliament elections.

Mr Farage has four children: Two boys by his first wife and two girls by his German second wife Kirsten. His interests include cricket and fishing. Despite his wealthy background, he prides himself on keeping up with the concerns of ordinary people.

But while Mr Farage's "people's army" could win a handful of seats nationally, that is unlikely to be enough for the party to call the shots over the EU referendum.

The kingmaker - Scottish National Party leader Nicola Sturgeon

Steely and polished Scottish independence leader Nicola Sturgeon has emerged as an unlikely star of the race and could yet decide who becomes prime minister.

Ms Sturgeon's formidable performances in election debates have made her one of the most talked-about figures in the campaign - despite not running for a seat in Westminster herself.

The Scottish First Minister has criticised austerity and advocated the Scottish National Party (SNP) as a "progressive force", with a quick humour that has cut a swathe through Britain's male-dominated politics.

She is the most popular political leader in Britain, according to a poll, which gave her a 33 per cent approval rating compared with Prime Minister David Cameron's 7 per cent.

The 44-year-old was born in the industrial town of Irvine, south-west of Glasgow, in 1970 to an electrician father and a mother who is still active in SNP politics. She joined the party at 16.

She studied law at Glasgow University and, at 21, stood unsuccessfully for the House of Commons in 1992, before starting her career as a lawyer.

When the Scottish Parliament was created in 1999, Ms Sturgeon entered as one of its first wave of lawmakers.

After voters rejected Scotland independence in a referendum last year, Ms Sturgeon took over as SNP leader from her mentor Alex Salmond, becoming Scotland's first female first minister.

Although it failed to win independence for Scotland, the SNP has enjoyed a surge in support. The party is expected to oust Labour from its traditional strongholds in Scotland and become the third-largest party in the British Parliament.

Neither the Conservatives nor Labour are predicted to win enough seats to govern alone - and Ms Sturgeon has offered to help Mr Miliband become prime minister.

With input from Reuters, Agence France-Presse