UPDATE 5-TV debate victory might not boost Scottish independence leader
* Scotland to hold independence referendum on Sept. 18
* TV debate seen as last chance to reach wide audience
* Snap poll showed nationalist leader easily won
* But suggests impact of win could be limited (Releads, adds poll, currency debate details)
GLASGOW, Scotland, Aug 26 (Reuters) - A convincing win by Scotland's pro-independence leader Alex Salmond in a final TV debate ahead of next month's breakaway referendum might not be enough to revive his campaign's chances of victory, a snap poll suggested.
In Monday's bruising encounter ahead of the Sept. 18 ballot, Salmond relentlessly talked over Alistair Darling, head of the "Better Together" camp, arguing Scotland would be wealthier, freer and better governed if it went it alone.
With the campaign to break up the United Kingdom and sever Scotland's 307-year union with England trailing in opinion polls by an average of up to 14 percentage points, Salmond's supporters were hoping for a game-changing performance.
A snap Guardian/ICM poll showed 71 percent of 505 people in Scotland who watched the debate judged that he had won.
However, the same survey suggested this would not alter the outcome of the referendum, with the number of people who said they would vote "yes" (49 percent) and "no" (51 percent) remaining unchanged despite Salmond's strong performance.
Professor John Curtice of Strathclyde University, a polling expert, said it was far from certain that the nationalist leader's victory would translate into a win at the ballot box.
"While Salmond was the obvious winner, it doesn't seem to have moved votes at this stage," he said.
If Scotland, with its $250-billion (150-billion-pound) economy, 5.2 million people, oil industry, and nuclear submarine base, leaves Britain, with its $2.5 trillion economy and 63 million people, the consequences would be profound.
Britain's three main political parties want it to stay in the union, which includes England, Wales and Northern Ireland.
Scotland's press, parts of which have traditionally been hostile to Salmond, recognised his debate win. "Salmond Bounces Back," said the Daily Record, the second best-selling newspaper, while the top-selling Sun said Darling had been "smoked".
Several recent polls have shown support for independence pushing higher, but the most recent "poll of polls", on Aug. 15, which was based on an average of the last six polls and excluded undecided respondents, found support for a breakaway stood at 43 percent against 57 percent for remaining within Britain.
Although Salmond, the leader of the Scottish National Party (SNP), got more cheers than Darling in Glasgow, Scotland's biggest city, he didn't land a knock out blow.
Instead, over the course of a scrappy hour-and-a-half, he asked Darling the same questions again and again, a tactic which unsettled the former British finance minister.
"The eyes of the world are indeed focused on Scotland," Salmond told the audience in an emotional opening statement, urging Scots to vote for full independence. "This is our time, our moment. Let us do it now."
Scotland's health service would do better under independence, he argued, questioning whether the British government would give Scotland any more devolved powers.
Scotland already has its own parliament with control over policy areas such as education and health.
Darling, who voters judged to have won a previous TV debate on Aug. 5, failed to field his opponent's questions with the same poise this time and struggled to get his points across in the face of concerted barracking from Salmond.
In the last clash, Salmond came unstuck on what currency arrangements an independent Scotland would use. He advocates a pound-sharing currency union, but has struggled to explain what he would do if what was left of Britain refused that option.
All three major British parties have ruled out such a union. Salmond predicts that would change if there was a "yes" vote.
This time, Salmond was more expansive, saying he had three "plan Bs" if he couldn't get his preferred option including shadowing sterling or having Scotland's own currency.
"We cannot be stopped from using the pound anyway," he argued, to loud applause from supporters in the audience.
Darling dismissed as "nonsense" the idea of using sterling informally. "He can't answer basic questions on currency. He can't answer basic questions on tax and spend," he said.
He ended by repeating the anti-independence campaign's slogan, telling Scots they could have the "best of both worlds".
"We do not need to divide these islands into separate states in order to assert our Scottish identity," he said.
Salmond urged voters to grab "with both hands" what he termed a unique opportunity that might never repeat itself. (Writing by Andrew Osborn; Editing by Crispian Balmer)