As the conference season ends, which leader faces the toughest task?

Ever since he burst onto the political scene during the Tory leadership election five years ago, David Cameron has consciously or otherwise modelled himself on Tony Blair.

To begin with, he appeared to invite the comparison, describing himself as the "heir to Blair" at a dinner with a group of newspaper executives in October 2005.

One of the newspaper editors present on that occasion reputedly warned him: "David, I would not repeat that outside this room," and to be fair to Mr Cameron, he took the advice.

But though the Prime Minister is nowadays more keen to play down the comparisons, this week's Conservative Conference in Birmingham showed they have not gone away.

Political blogger and former North-East Labour official Hopi Sen produced a fascinating comparative study of Mr Cameron's conference speech on Wednesday with Mr Blair's first address as Prime Minister in 1997.

For instance, in 1997, Mr Blair said: "When people say sorry, that’s too ambitious, it can’t be done, I say: this is not a sorry country, we are not a sorry people. It can be done."

Fast forward to this year, and Mr Cameron is telling us: "Don’t let the cynics say this is some unachievable, impossible dream that won’t work in the selfish 21st century – tell them people are hungry for it."

And as Hopi points out: "In Blair’s first speech we find a young girl who writes in to say how much she liked going to a summer camp. In Cameron’s a young girl writes in to help pay off the deficit."

But what really unites Messrs Cameron and Blair is not so much their shared rhetorical style or even their presentational skill, but their tendency to want to define themselves in opposition to their own parties.

Mr Blair loved nothing better than to don the Tories' clothes – whether it was being tough on crime, a hawk in international affairs, or even privatising public services when Gordon Brown would let him.

He knew it wound his party up – but that was fine so long as it showed the wider electorate that Labour was no longer hidebound by what he saw as out-of-date ideology.

Now we have Mr Cameron wanting to make 'fairness' the defining characteristic of his government – not a value with which the Tories have always been readily associated.

The Prime Minister knew that the decision to axe child benefit for households with a higher-rate taxpayer would wind-up his own grassroots – but what mattered was whether the wider public saw it as fair.

But did they? It certainly doesn't appear to be very "fair" to families with a single-earner in the higher tax bracket whose partner stays at home – and may well have to be rethought for that reason.

Culture secretary Jeremy Hunt then broadened the debate by raising the issue of whether the state should subsidise people who have more and more children.

Was it a gaffe - or was he acting as an 'outrider' for Mr Cameron, in the way that Stephen Byers and Alan Milburn sometimes used to do for Mr Blair, saying the things the leader dare not say himself?

Time will tell – but as the post-election conference season draws to a close, how do the three parties and their leaders currently stand?

Labour's Ed Miliband must persuade a sceptical public he is a better leader than his brother would have been. Nick Clegg has to win that referendum on voting reform, or risk the Lib Dems being flattened at the next election.

As for Mr Cameron, he must convince the voters that the most savage spending cuts to be unleashed for decades are somehow "fair."

It is hard to say which of the three of them faces the most difficult task.