A change or more of the same?

The phoney war is over. After months of skirmishing, battle has finally been joined for the most closely-fought general election since 1992.

The Conservatives are portraying it as a watershed election, comparable to 1979 when Margaret Thatcher came to power or even Tony Blair's 1997 landslide.

According to David Cameron, it will be an opportunity for a fresh start, throwing out a government that has virtually bankrupted the nation and presided over the longest recession in living memory.

Gordon Brown will be arguing that with fragile green shoots of recovery emerging, this is no time to be taking a gamble on a novice.

He will present himself as the steady, weather-beaten pilot who has steered the ship away from the rocks - even though his opponents claim his policies as chancellor holed the economy below the waterline.

With opinion polls suggesting a strong likelihood of a hung Parliament - with neither Labour nor the Conservatives securing an overall majority - the Liberal Democrats find themselves in the position of potential kingmakers.

Their leader Nick Clegg will appear alongside Mr Cameron and Mr Brown in the three televised leaders' debates.

It will temporarily elevate him to the status of a "prime minister-in-waiting", helping the Lib Dems counter the traditional argument that a vote for them is a "wasted vote".

Labour knows that it goes into this election as the underdog. After three terms in power, it is vulnerable to charges that it is tired and running out of steam.

That would have been the case even if it had not presided over a catastrophic economic collapse, which saddled the country with levels of debt that will take generations to pay off. Mr Brown's claims when chancellor to have abolished boom and bust seem pretty hollow now.

All Labour's effort will be focused on trying to prevent the election becoming a referendum on Gordon Brown and Labour's record.

Instead, they want to make it a choice between a Labour government which can point to the first signs of economic recovery and a Conservative government whose policies could tip the UK back into recession.

For all Mr Cameron's success in modernising his party and hauling it back from the depths of its unpopularity, critics claim he has failed to spell out a clear message of what he would do in power.

There was an embarrassing wobble at the start of the year over the proposed tax break for married couples, with even Mr Cameron admitting he "messed up".

The row over the tax status of Lord Ashcroft, the billionaire Tory donor, was allowed to fester. It exploded in Mr Cameron's face weeks before the election was called - and allowed Labour to claim the Conservatives were still a party that looked after its rich friends.

Mr Brown has demonstrated a dogged and ruthless determination to hold on to power, swatting away critics and re-assembling many of the team that helped Labour win in 1997, including Lord Mandelson and Alastair Campbell.

They have lost none of their visceral determination to keep the Tories out of No 10 - and have often managed to run rings around a better financed but less experienced Tory team.

A Labour win will be a formidable achievement, triumphing over all expectations that a government which has presided over such an economic slump should be thrown out of office. If Mr Brown achieves the near impossible - or even denies Mr Cameron an overall majority - it will be because of doubts about the Tories.

It is often said that governments lose elections. But oppositions also have to be credible and be seen as a government-in-waiting.

Mr Cameron enters the election still having to "seal the deal" with voters. There is no sign yet that he has generated the wave of enthusiasm and yearning for change Tony Blair achieved in 1997 for New Labour.

The Tories' warnings of an "age of austerity" with tough measures to cut the deficit more quickly than Labour appeared to have frightened some voters.

So now it has been softened, with a promise to block Labour's National Insurance increase for low and middle-income earners. But it has resulted in a confused message - with the Tories' opponents asking: "How can you cut taxes and repay debt at the same time?"

The wild card will be the three prime ministerial debates, a real innovation bringing the hustings into the living rooms of voters.

The party leaders have been prepping themselves for weeks, knowing that a slip-up could wreck their chances.

Mr Cameron is undoubtedly more comfortable on television than Mr Brown, who often appears more defensive, taking refuge behind a barrage of statistics.

But Team Brown have had considerable success recently in presenting a more human image of the Prime Minister - and claims that he bullied staff appear to have helped rather than hindered, suggesting a strong personality.

The Tories' theme "time for a change" is one of the most durable election slogans and it certainly trumps "more of the same".

Mr Cameron is convinced that if the voters are asked "Do you want another five years of Gordon Brown?", the answer will be "No".

Mr Brown is counting on voters opting for the old nursery room saying: "Hold on to nanny for fear of something worse."