"We are now in a de facto multi-party system," said Simon Hix of the London School of Economics (LSE). "A third vote Conservative, a third vote Labour, a third vote somebody else."

The BBC's opinion poll tracker currently puts the centre-right Conservatives on 34 per cent and centre-left Labour on 33 per cent, followed by the anti-EU UKIP, junior coalition partners the Liberal Democrats, the Greens and a string of other parties.

As if that were not complicated enough, the election is also bringing into focus two important ways in which Britain's identity could change in the coming decades.

Britain's future in the European Union could be in play. And nationalist parties, particularly the pro-independence Scottish National Party (SNP), look set to make major gains, which could hasten the loosening and eventual break-up of the United Kingdom. Support for the SNP has surged even though Scotland voted against independence in a referendum last year.

Former SNP leader Alex Salmond makes no bones about now bringing the fight to London.

"The stars are moving into alignment," Salmond said while out campaigning in the town of Ellon in northeast Scotland, where he hopes to win a seat in the House of Commons.

"Scotland has an opportunity to have decisive influence in the Westminster parliament.

"So I thought given these circumstances it would be foolish not to try and put my shoulder to Scotland's wheel and push it on."

The 60-year-old was leader of the Scottish National Party (SNP) for 20 years and first minister of the devolved government in Edinburgh for seven, before stepping down after the independence referendum.

Voters rejected his long-cherished dream of an independent Scotland by 55 per cent to 45 per cent. But anybody who thought that was the end of Salmond underestimates the ambition of the man, who is viewed by his supporters and critics as one of the most talented politicians of his generation.

"The dream will never die," he told supporters after the results of the September referendum came through.

The SNP is expected to win most of Scotland's House of Commons seats in May and insists it could be prepared to prop up a minority centre-left Labour government in return for key concessions.

The SNP is offering to support the centre-left party in government on a vote-by-vote basis as long as that keeps Prime Minister David Cameron's Conservatives out of office.

"The UK is now evolving towards a quasi-federal country," said the LSE's Tony Travers.

Travers added that the SNP's main objective "would not be to produce a stable government in the UK - it would be to have another referendum on Scottish independence".

"Our first move if there's a Tory minority government will be to move to bring it down," Salmond said, most likely by voting against its first budget.

Such combative statements are typical of Salmond, and the idea of playing kingmaker appeals to many Scots who complain that for too long they have been treated in Westminster like England's poor relation.

Then there is the possibility that Britain could end up leaving the European Union as a result of the election.

Cameron has promised to hold an in-out vote by 2017 if the centre-right Conservatives win outright on May 7.

While none of the main parties are making Europe a big issue in a campaign dominated by the economy and the future of the state-run National Health Service (NHS), polls suggest an EU referendum could be relatively close.

The latest YouGov poll in February found that support for membership was at an all-time high of 45 per cent against 35 per cent in favour of leaving.

The popularity of the UK Independence Party under leader Nigel Farage played a major part in prompting Cameron to make the 2017 referendum promise.

But UKIP looks unlikely to win enough seats to be able to prop up a minority Conservative government and force it to hold an EU referendum this year, as Farage wants.

Farage's future as UKIP leader depends on whether he can persuade voters in South Thanet to vote him in, while also leading the party's national campaign. He has said he will quit as leader if he fails to win the seat.

He has a fight on his hands - a poll commissioned by the party and leaked to this week's newspaper put Farage one point behind his Conservative rival.

While dismissing the figure as "rogue", a UKIP spokesman added: "No one is pretending we do not have work to do."

The potential departure of Farage from the political arena would be a major loss for UKIP, for whom Farage has been the party's acceptable face.

He avoids the kind of race-related gaffes for which the party has expelled a string of members - although he has previously voiced admiration for Russian President Vladimir Putin and suggested foreigners with HIV should not receive treatment on the state-funded National Health Service (NHS).

Farage isn't the only big name in British politics who could lose their jobs after the election.

Hix predicted that Cameron would resign as Conservative leader if the party lost, while Labour would force Miliband to do the same if he failed to get into Downing Street after five years of austerity.

Deputy Prime Minister Nick Clegg, whose centrist Liberal Democrats are the coalition's junior partners, has seen his party's support slump to single figures in government and could even lose his own seat, according to the polls.

But many Britons could be more interested in a totally different kind of celebrity come May.

Kate, wife of heir to the throne Prince William, is due to give birth to the couple's second baby later this month, an event with more than enough pageantry and razzmatazz to eclipse anything on offer in the gloomy corridors of the parliament at Westminster.

CAMERON’S DO OR DIE

While British Prime Minister David Cameron's government has overseen deep austerity cuts, he personally has attracted flak for what opponents see as an overly relaxed approach to his job.

In a phrase that stuck, one aide, not among his critics, told biographers: "If there was an Olympic gold medal for chillaxing, he would win it."

But some 47 per cent of Britons believe Cameron is doing well as prime minister, according to a recent YouGov/ poll, making him the most popular of the main party leaders. By comparison, the Conservatives are currently polling in the low 30s.

That failure to shake off the Conservative Party's image as the "nasty party" could cost Cameron his job.

Cameron's own background and the party's emphasis on cutting benefits as part of its austerity programme has fuelled criticism that his party only represents the privileged.

The son of a stockbroker, Cameron was educated at Eton, the school later attended by Princes William and Harry, and Oxford University.

After university, Cameron worked for the Conservatives as an adviser before a stint in public relations, which ended when he was elected to parliament in 2001.

Cameron rose swiftly within the Conservatives - then struggling badly against Tony Blair's Labour government - and was elected leader in 2005.

After winning the leadership at the age of 39, he tried to "detoxify" the party brand by avoiding traditional right-wing issues such as immigration.

At the 2010 general election, Cameron became the youngest prime minister for 200 years, but the Conservatives did not win enough seats to avoid having to form a coalition. Instead, they had to team up with the centrist Liberal Democrats for Britain's first coalition government since the second world war.

MILIBAND’S SURPRISING SURGE

Despite an awkward public image and the dark story of his rise to power, British opposition leader Ed Miliband is confounding critics ahead of an election that could make him prime minister.

The 45-year-old, long seen as a drag on the Labour party's chances and the target of leadership coup rumours just a few months ago, has matched up surprisingly well against Conservative leader David Cameron in the campaign.

"I've been underestimated at every turn," he said in a fiery exchange with a fearsome interviewer, Jeremy Paxman, during a TV grilling alongside Cameron last month.

"Hell yes I'm tough enough!" he added in response to another Paxman question in a session that one poll showed him winning by 25 per cent to the prime minister's 24 per cent.

Miliband still has no shortage of critics.

The right-wing press has branded him a diehard left-winger - "Red Ed" - while Cameron and others have upbraided him for the banking deregulation that occurred while he was working at the Treasury in the years before the financial crash of 2008.

Much has also been made of the fact that his house in London's well-off Dartmouth Park neighbourhood is big enough to have two kitchens, and of his much-mocked struggle to eat a man-of-the-people bacon sandwich in front of photographers.

For a man with a nasal voice who used to wear Harry Potter-style glasses and who is portrayed by The Guardian's cartoonist as a grinning "Wallace" from Wallace & Gromit, the geek image is hard to shake off.

Perhaps most damaging, however, is the family rift that the fiercely ambitious Miliband created by taking on and beating his older brother David, a protege of former prime minister Tony Blair, for the Labour party leadership in 2010. Miliband himself said recently that the divisions are now "healing".

Agence France-Presse

FARAGE’S APPEAL TO PAST

Rarely photographed without a pint of beer in hand, Nigel Farage has turned the UK Independence Party into a national force but is battling for his future at Britain's May 7 election.

Anti-Brussels and anti-political correctness, 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.

The 51-year-old, who once compared ex-European Council president Herman Van Rompuy to a "damp rag", led UKIP to victory in last year's European elections and third place in opinion polls before May's vote.

Farage was born in 1964 to an affluent family in Kent, southeast England. His father was a stockbroker and an alcoholic, and his parents divorced when he was five.

He was educated at one of England's top private schools, Dulwich College, where he says his headmaster saw him as "bloody-minded and difficult".

Rather than attending university, he followed his father into the City of London, where he says that 12-hour boozy lunches were the norm.

Having supported the Conservatives since his school days, he joined UKIP in 1993 as a founder member and was elected to the European Parliament in 1999, aged 35.

Farage became UKIP's leader in 2006 before standing down in 2009 and then being re-elected the following year, when UKIP's ascent really began.

He has survived a string of personal misfortunes - a serious car accident, testicular cancer and a plane crash as he was campaigning during the 2010 general election.

Farage is married to a German woman and has four children. His interests include cricket and fishing.

He prides himself on keeping up with the concerns of ordinary people in the "pubs, coffee mornings and yes, even the golf clubs of Britain". This backfired last month when he and his family were chased out of his local pub by anti-UKIP protesters he labelled "scum".