What's at stake for leaders?

Analysis
By Nick Assinder
Political correspondent, BBC News website

Tony Blair may be the man in many voters' sights when they go to the polls across Britain but, of all the main UK party leaders, he probably has the least to lose.

Mr Blair will soon be saying his farewells

The prime minister may not relish the prospect of the good "kicking" he believes is awaiting him, but he is already on the way out.

So, neither his future leadership nor the timing of his departure will be directly affected by the outcome of the polls.

At least no more than the election date was a factor in his calculations over when best to make his final announcement.

Undoubtedly, he would have liked his final days in office to be marked by something other than a poll defeat, and he will spend his last weeks in power attempting to offset the likely results with some "positive messages".

These will include things such as the expected creation of the new Northern Ireland assembly on 8 May.

Indeed Mr Blair has already announced he will clarify his plans - in other words announce his departure - next week.

It is then expected he will embark on a seven week or so "farewell tour", as Labour chooses his successor.

Set the seal

Those seven weeks include summits at which Mr Blair will hope to broker an international climate change deal, and possibly help engineer a treaty covering the EU's future.

Mr Cameron needs to prove Tories are back

Had he not been leaving office, a significantly bad result in the Scottish, Welsh and local polls would undoubtedly have seen calls from some on his own side for him to quit.

And even though he is going, a bad result is not the way he would have wanted his tenth anniversary to be marked or his premiership to end.

The elections also present major challenges for the other leaders.

David Cameron's Tories are enjoying what appears to be a genuine revival, with rising poll showings and the growing belief amongst his MPs they really can win the next general election.

He needs to underpin that by seizing the advantage offered by Mr Blair's unpopularity and show the Conservatives are now the natural choice for disillusioned or dissatisfied voters.

He needs to win something in the region of 500 to 600 seats in the polls.

But he will also want to see signs that the party is turning the tide in northern English cities, and Scotland, as well as significant gains in Wales, to show that he is on track to win the next General Election.

Hardest areas

In Scotland it is the SNP which is riding high, capitalising on Labour's woes, and leader Alex Salmond has a real chance of becoming first minister, or at the least leader of the largest party.

Sir Menzies leadership is still an issue

But Mr Cameron's Scottish Conservative Party will need to increase its showing in the parliament to help show the new leader is broadening his party's appeal and fighting back in even the hardest areas.

Good elections for the Tories would help silence those internal critics who oppose his direction of travel and would secure his already-solid position.

While his main battle is with Labour, there is a secondary battle which is arguably just as important, with the Liberal Democrats.

The third party has already made advances in councils and assemblies across Britain as voters have turned away from Labour, but refused to go straight to the Tories.

Mr Cameron needs to show he is changing that, particularly with a glimpse of hope in Scotland, to prove his party is not becoming an English-only one.

A good showing would also provide the backdrop to his ongoing policy reviews which will have to start producing some concrete proposals if he is to avoid the charge of being all show and no go.

Question marks

Liberal Democrat leader Sir Menzies Campbell, on the other hand, also has a big challenge ahead of him.

>His leadership may have settled down a bit of late, but there are still some real doubts about him with voters and, more worryingly, within his own party.

There is the historic fear that a reviving Tory party will inflict the same squeeze that has previously seen the third party denied the longed-for political breakthrough.

Mr Brown will attempt a Labour renewal

The party currently wields power, either on its own or in co-operation with others, in regions right across the country and much is made of its record, in particular, in Scotland.

But hanging on to that position will probably not be enough to remove any question marks over Sir Menzies' leadership.

He will need to improve things, and most crucially show that the gains made over the past years will not be reverse by the Tories.

Failure to do that will almost certainly lead to new grumblings over his leadership and may even see attempts to replace him before the next general election.

Salmond and Wyn Jones

The battles in Scotland and Wales will also prove significant for nationalist leaders - the SNP's Alex Salmond and Plaid Cymru's Ieuan Wyn Jones - both of whom believe they can end up in power.

Mr Salmond, in particular, has a lot riding on his party's apparent surge in popularity which could propel him into the job as first minister, although thanks to the PR electoral system, it would have to be in coalition with another party, likely the Liberal Democrats.

Mr Wyn Jones also claims his is the party which can defeat Labour - despite the fact that Labour's Rhodri Morgan has put "clear red water" between himself and Tony Blair's government - so he will need to fulfil that promise, again in a coalition though.

Finally, there is the leader - and prime minister - in-waiting, Gordon Brown, who finally has the leadership within his grasp.

Many of his supporters have been furious that Tony Blair has, in their view, hung on to power for too long and made it harder for Mr Brown to halt Labour's slide.

The chancellor's job will be to weather a bad election result, let Tony Blair take the blame, and start a process of Labour's "renewal in power".

He will hope the polls will act as a turning point for Labour, allowing voters to express their dissatisfaction but then stick with the party as it embarks on a new phase.