Analysis By Nick Assinder Political correspondent, BBC News website

So who will get the best reception at this year's Liberal Democrat conference - current leader Sir Menzies Campbell or his predecessor Charles Kennedy?

Sir Menzies has to reassure his party

It may not be the biggest question the party wants to address as it gathers in Brighton.

Sir Menzies has already insisted he is not expecting any "Gary Cooper High Noon" at the conference.

But that, along with a core debate on taxation, is the issue that is already hanging over the event.

The vote over the new leader's central policy of abandoning Mr Kennedy's 50p top tax rate policy in favour of his own green tax proposals is the debate likely to give Sir Menzies the biggest problem although he insists losing would not represent a threat to his leadership.

It has become the single biggest issue to symbolise a shift away from the previous leader's stance and stamp the new man's identity on the party, which has still not entirely recovered from the brutal and bitter removal of Mr Kennedy over his drinking problem.

So the outcome of the vote on this policy will be seen as the clearest indication of whether Sir Menzies has finally got a grip on his party and moved on from his predecessor's era, or whether grassroots members still hanker after the man who took them to great electoral success in the past two general elections.

Party bosses seem confident they will win the vote and, as a result, finally draw a line under the leadership issue which has continued to dog Sir Menzies since the damaging contest earlier in the year. Indeed, some even seem to be relishing a showdown.

Leadership challenge

Anything Mr Kennedy has to say on the issue might prove pivotal, although it is thought unlikely he will openly oppose it.

Kennedy is still held in high regard

If the new policy is thrown out by the conference, however, Sir Menzies will be put under immense new pressure and a leadership challenge before the next general election - already being whispered about in some quarters - will start looking like a real possibility.

Despite continuing good local and by-election results, the new leader has struggled to make his mark and faced persistent claims that he lacks the popular touch and energy of his predecessor.

There is a fear among many Lib Dems that, with David Cameron's Conservatives moving into the centre ground, the party will lose momentum and identity and could slip back into its old position as a poor third in parliament.

And then there will be the two men's big speeches - Mr Kennedy will address the conference on Tuesday, shortly after the tax vote, and Sir Menzies will bring it to a close on Thursday.

Lot to prove

Mr Kennedy's performance is already being branded his "comeback" speech which will show he has overcome his drink problem and is ready for a place on the frontbench, perhaps in the next re-shuffle.

Hughes suggested leader would be judged

But his words will be pored over for any sign of his feelings towards Sir Menzies and whether, as some have suggested, he harbours ambitions to once again lead his party.

As for Sir Menzies - his first big conference speech as leader needs to be a bit special. He still has a lot to prove to his party and the wider world.

Earlier this year he was forced to slap down failed leadership contender Simon Hughes for suggesting he would be "judged" at this year's autumn conference.

He has managed to up his game in the Commons and, after a very shaky start, is once again being seen as a serious, heavyweight and statesmanlike performer.

He will need to underpin that in his big speech while giving the party a clear sense of direction and reassuring the grassroots that he will be able to lead them to even greater electoral success.

He will want to leave Brighton with all the questions and concerns over his leadership style and policy direction finally answered.

Nick.Assinder-INTERNET@bbc.co.uk