British Prime Minister David Cameron is battling to win a second term in power that could define his legacy -- potentially as the man who led his country out of the European Union.

Cameron's Conservative party -- once led by "Iron Lady" Margaret Thatcher -- is currently at level pegging in opinion polls with the main opposition Labour Party.

And even if Cameron nominally wins the May 7 election, he looks unlikely to be able to achieve his aim of ditching his Liberal Democrat coalition partners and governing alone.

While 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."

A former Conservative deputy chairman turned pollster, however, wrote recently that "uniquely among the leaders, he (Cameron) commands higher approval ratings than his party".

"But this signals that, in important respects -- at least in the eyes of voters -- Cameron has not been able to change the party he leads," Michael Ashcroft added.

Some 47 percent of Britons believe Cameron is doing well as prime minister, according to a YouGov/Sunday Times poll this week, 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.

'Detoxifying' the Conservatives

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, where he was admitted to the Bullingdon Club, a hard-drinking, socially exclusive student group.

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

Cameron rose swiftly in 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 like immigration and stressing a more liberal agenda.

He posed with husky dogs at the North Pole to highlight his green credentials, while his respect for public services was underlined by the care his disabled son Ivan received from the state-run National Health Service (NHS).

Ivan, who had cerebral palsy and severe epilepsy, died aged six in 2009.

Cameron is married to Samantha, a design executive, and the couple have three surviving children.

Marriage of convenience

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 World War II.

At home, the coalition has been defined by its spending cuts, while foreign policy was dominated by wrangling over Britain's role in the EU.

Abroad, following long military campaigns in Iraq and Afghanistan, Britain played a smaller role on the world stage under Cameron.

In 2013, his plan to join international military action against the Assad regime in Syria was defeated by the House of Commons, although Britain did join operations in Libya in 2011.

Last year, Cameron avoided becoming the leader under whom Scotland split from Britain after Scots rejected independence in a referendum, despite a last minute surge by the "Yes" camp.

Winning as worst outcome?

While the coalition government brought stability for Britain, albeit through a series of compromises, it did not make the Conservatives popular.

Despite an economic recovery, outright defeat on May 7 is a real possibility for Cameron, as is five more years in a coalition or minority government.

Cameron has said that if re-elected he will not carry on as prime minister beyond 2020.

The election will determine how history judges him, not least because it will dictate whether there is a referendum on Britain leaving the EU.

Cameron promised to hold a referendum by 2017 under pressure from eurosceptic Conservative MPs frustrated by Cameron's liberal outlook and failure to lead them to a clear election victory last time round.

Even if the Conservatives do win next month, the coming years could be hard.

"The worst case scenario for Cameron in 2015 might be winning the general election with a very small majority, leaving him prey to the whims of his eurosceptic and right-wing backbenchers," political historian Anthony Seldon has written.