* Final TV debate seen as opportunity for both camps
* Poll showed nationalist leader lost first TV debate
* Independence movement still behind in the polls
* Both sides chasing undecided voters before Sept. 18 vote
By Alistair Smout
EDINBURGH, Aug 25 Scotland's future will be debated in a final TV showdown on Monday just weeks before a historic independence referendum with the pro-breakaway camp, behind in the polls, looking for a game-changing performance from its leader.
As voting day, Sept. 18, draws nearer, polls show that the campaign to sever Scotland's 307-year union with England and leave the United Kingdom is trailing in the polls, as it generally has been from the start.
Several recent polls have shown its support climbing a few points, but according to the most recent "poll of polls" on Aug. 15, based on an average of the last six polls and excluding undecided respondents, support for the pro-independence camp stands at 43 percent against 57 percent for opponents.
However, Alex Salmond, the leader of the pro-independence Scottish National Party (SNP), enjoys a reputation as a canny campaigner who has unexpectedly won elections in the past.
"It's the last real public chance to reach a large audience," Patrick Brione, director of research at pollster Survation, said of Monday's TV debate.
"Salmond is very much the underdog at the moment, so he really needs to pull off an impressive performance."
The debate is expected to centre on three issues: if and how an independent Scotland could keep the pound, how many barrels of oil are left in the North Sea, and whether Scotland's publicly funded health service would be better off in a breakaway state.
Salmond unexpectedly failed to dominate the first such TV debate, on Aug. 5, in which Alistair Darling, the leader of the anti-independence "Better Together" campaign, put him on the spot over the issue of currency arrangements in an independent Scotland.
The question is one that opponents of independence have long pushed for an answer to. Yet Salmond seemed blindsided by Darling's persistence and failed to spell out what his "plan B" would be if the British government refused to formally share the pound, his preferred option.
All three major UK-wide parties have ruled out such a union; Salmond predicts their position will change if there's a "yes" vote.
"Going into the previous debate he was the favourite, and as a result of that people thought that he lost the debate," Survation's Brione said of Salmond.
"Darling benefited very much from people not expecting him to do well going into the first debate. His performance, however good as it was, was made to look better."
According to a snap poll, Darling, seen as a safe pair of hands but as somewhat uninspiring, won that debate.
Salmond has said he wished he'd better explained his currency plans and has promised to do so in Monday's debate.
A spokesman for the pro-independence "Yes Scotland" campaign said on Sunday the debates were important because they reached a very large audience. But he emphasised the breadth of the movement's grassroots campaign, which he said gave it an edge.
Douglas Alexander, the Labour party's foreign affairs spokesman and an opponent of independence, said the nationalist campaign was in trouble.
"For them to be in a position with just days to go until postal ballots drop where they cannot answer the most fundamental question in relation to what currency Scotland would use... is genuinely not where they expected to be," he said.
The debate, which will be held in an art gallery in Glasgow, will be shown at 2030 BST (1930 GMT) on the BBC, and unlike the first debate, will be broadcast in the rest of Britain. (Reporting by Alistair Smout; Writing by Andrew Osborn; Editing by Stephen Powell)