By James Landale
Deputy political editor, BBC News
Nick Clegg, Gordon Brown and David Cameron
Two down, one to go. Thursday's third and final election debate is important.

It is the closest to polling day and will be watched by many people who have yet to decide how to vote.

What the three party leaders say and how they perform will influence the decision that these voters make. In other words, this debate could make all the difference. At the same time, the nation will be transfixed as Gordon Brown eats humble pie – again – for being rude about a woman, Gillian Duffy, who has fast become the media's favourite granny. It will be excruciating.

Here are a few general thoughts:
1. Duffygate – or bigotgate – will hang over the debate but will not dominate it.

Gordon Brown will have to deal with the encounter but Messrs Cameron and Clegg will be quite happy to let him squirm without being seen to add to his distress. They know how easily the taunting of Mr Brown over bullying allegations and ill-scripted condolence letters engendered public sympathy rather than opprobrium.

2. The novelty factor will be less salient this time.

The first debate was historic and its outcome utterly unpredicted. The second, though, was less surprising. So there might be less focus on the body language, the format, the clothes, and perhaps a little more on what the leaders actually say.

3. The debate is important because the subject is the economy, arguably the most significant policy issue of the election.

Many voters will want the leaders to cut to the chase. All three will be asked what must now be known as the Institute for Fiscal Studies question: namely, what are you going to cut and when? They will not answer to the satisfaction of some. There will be an inconclusive debate about the dangers of a Greek-style financial meltdown taking place in Britain.

4. This is Gordon Brown's last chance to get Labour's campaign back on track.

The economy is his strongest card. This is his moment to seek redemption. He will argue that public spending must be maintained this year to protect the recovery and that government must intervene to support new industries. He has to hope that voters think his plans for the economy are more important than the sincerity of his penitence.

5. Voters who have been impressed by Nick Clegg will watch and consider whether they should now vote for him as well.

The Lib Dem leader needs to maintain momentum into the last week of campaigning. Many voters told the opinion pollsters after the first two debates that they liked the cut of his jib. Mr Clegg's task now is to persuade those people that they should stick with him and give them their vote – without appearing as if he was taking them for granted. He has admitted already that voters will be more “demanding” this time around.

6. Nick Clegg will have to clear up what he would do in a hung parliament.

He said initially that he would not support Labour if it won most seats but had fewer votes than the Lib Dems or Tories. He then suggested that he might support Labour in those circumstances – but only if the party ditched Gordon Brown. He then pulled back a bit and said he would work with the man on the moon if he delivered greater fairness. David Cameron will push him hard on this, claiming that if you vote Clegg, you could get Brown. The Tory leader will also try to warn voters that a hung parliament might not be the utopia of congenial cooperation that many seem to think it might be.

7. This is David Cameron's last chance to try to explain what he means by a “big society”.

It is a radical programme that would in theory transform huge swathes of public life but many voters are still struggling to understand what the phrase means. His challenge is to boil it all down into something that makes an impact and excites the public as much as the policy wonks. This is a tough ask in the context of a debate.

8. Immigration has come up in the previous two debates and Gillian Duffy has ensured that it will come up again.

This will not help Gordon Brown. He will have to persuade voters that it is not bigoted to be concerned about immigration, despite what he said about Mrs Duffy. Nor will it help Nick Clegg. He has appeared vulnerable at times when explaining his policy of granting an amnesty for hundreds of thousands of illegal immigrants who have been in the country for more than ten years and speak good English.

9. Gordon Brown will have spent less time preparing than he will have liked.

An unexpected trip to Rochdale will have eaten into some of his prep-time. Maybe there will be fewer rehearsed lines. This could help rather than hinder.

10. David Cameron and Nick Clegg will be tempted to try some unfunny gags about Peppa Pig.

These will be incomprehensible to millions of voters who do not have young children or who did not catch Labour's clumsy attempt earlier this week to inveigle the children's television character into their campaign.

11. How many people will watch?
Nine million people tuned in for the first debate, some four million for the second. This time round there is a clash with Coronation Street on the other side. Who watches what will perhaps tell us a little about the state of British politics.

12.A member of the audience may be tempted to break their silence.

This is the third debate. It is the last before polling. People are getting used to the format. The ban on audience response is clearly frustrating. The temptation to clap or disagree noisily must be huge. Will anyone have the guts to break the rules?