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* Independence vote to take place on Thursday
* Polls show result too close to call
* Cameron makes last visit to Scotland before vote
* Pro-independence camp in confident mood (Relead, updates after speech)
By Guy Faulconbridge and Andrew Osborn
ABERDEEN/LONDON, Sept 15 (Reuters) - British Prime MinisterDavid Cameron used his last visit to Scotland before a historicindependence referendum this week to implore Scots to remainpart of the United Kingdom, warning on Monday that a breakawayvote would be irreversible.
With opinion polls suggesting the referendum remains tooclose to call, Cameron, the leader of the ruling Conservativeparty, which draws most of its support from England, pleadedwith voters not to use the referendum as a protest vote.
"There's no going back from this. No re-run. If Scotlandvotes 'yes' the UK will split and we will go our separate waysforever," he told an audience packed with Conservative partysupporters in Aberdeen, the centre of Scotland's oil industry.
"Don't think: I'm frustrated with politics right now, soI'll walk out the door. If you don't like me I won't be hereforever. If you don't like this government it won't lastforever. But if you leave the UK that will be forever."
Cameron's trip was a last-ditch effort to try to persuadeScotland's many undecided voters to reject independence. Up to500,000 people out of more than 4 million registered voters areestimated to be unsure how they will vote.
Campaigning in Scotland is fraught with difficulty forCameron, whose right-leaning party is unpopular with Scots whohave traditionally voted for the left-leaning opposition Labourparty and harbour bitter memories of former Conservative primeminister Margaret Thatcher's 1979-1990 stint in power.
Cameron's Conservatives have only one of 59 Britishparliamentary seats in Scotland, and the pro-independenceScottish National Party (SNP) has elbowed Labour aside in recentyears to emerge as the dominant political force.
Cameron, his voice at times faltering with emotion, spokeafter a video was shown extolling British achievements and someof the most prominent figures of British history from WinstonChurchill to Alexander Fleming, a Scot who discoveredpenicillin.
"Independence would not be a trial separation. It would be apainful divorce," Cameron said, standing in front of a giantUnion Jack flag and a poster saying "Lets stick together".
"Head and heart and soul, we want you to stay."
Cameron has conceded his public image as a privilegedEnglishman with aristocratic roots does not make him the bestperson to advocate against Scottish independence.
Scottish nationalists criticised him for staying away in theearly months leading up to the vote as complacent, and now thathe is showing his face, they portray him as a condescendingEnglishman in no position to advise Scots on how to vote.
Details of his visits north of the English border are notrevealed until the last minute for security reasons and criticssay his advisers try to minimise his contact with the public toavoid nationalist heckling. The visit was expected to last onlyhours.
CONFIDENT PRO-INDEPENDENCE LEADER
Alex Salmond, the pro-independence SNP leader, was outcampaigning too on Monday in Edinburgh where he met businessleaders who back the breakaway campaign.
He predicted Scotland would vote for independence and thatthe next time Cameron visited would be to discuss the details ofthe 5-million strong population's divorce settlement from theUnited Kingdom.
"The next time he comes to Scotland it will not be tolove-bomb or engage in desperate last-minute scaremongering,"Salmond said in a statement. "It will be to engage in seriouspost-referendum talks."
Independence supporters say it is time for Scotland tochoose its own leaders and rule itself, free of control fromLondon and politicians they say ignore their views and needs.
Cameron repeated the anti-independence "Better Together"campaign's core message: that by staying in the United Kingdom,Scotland can take advantage of the benefits of belonging to alarger, more influential entity while enjoying anever-increasing measure of autonomy.
"No" campaigners counter that Scotland is more secure andprosperous as part of the United Kingdom and say the end of theunion would destroy three centuries of bonds and shared historyas well as bring in economic and financial hardship.
Cameron's visit comes after David Beckham, the retiredfootballer, added his name to a petition of English celebritieswho say they want the Scots to stay.
The celebrity group, "Let's Stay Together", is organising apublic rally on Monday evening in London's Trafalgar Square.
It was the pro-independence camp's turn on Sunday night whena host of Scottish rock stars including the band Franz Ferdinandand Mogwai played a concert in Edinburgh.
Singer Amy McDonald told the audience: "People fight and diefor this (independence) and all we have to do is put a littlecross in a box. Scotland, you know what to do."
Opinion polls indicate the vote is hard to call.
Out of four recent polls, three showed those in favour ofmaintaining the union had a lead of between 2 and 8 percentagepoints. But an ICM poll conducted over the Internet showedsupporters of independence in the lead with 54 percent andunionists on 46 percent.
More than 4 million Scots as well as English and foreignresidents, from the Highlands and Islands to Glasgow's grittyinner city estates, are eligible to vote.
The question on the ballot paper will ask simply: "ShouldScotland be an independent country?" (Additional reporting by Alistair Smout and Angus MacSwan inEdinburgh and Sarah Young, William James and Kate Holton inLondon; Editing by Sonya Hepinstall)
