ABERDEEN/LONDON, Sept 15 (Reuters) - British Prime Minister David Cameron used his last visit to Scotland before a historic independence referendum this week to implore Scots to remain part of the United Kingdom, warning on Monday that a breakaway vote would be irreversible.
With opinion polls suggesting the referendum remains too close to call, Cameron, the leader of the ruling Conservative party, which draws most of its support from England, pleaded with voters not to use the referendum as a protest vote.
"There's no going back from this. No re-run. If Scotland votes 'yes' the UK will split and we will go our separate ways forever," he told an audience packed with Conservative party supporters in Aberdeen, the center of Scotland's oil industry.
"Don't think: I'm frustrated with politics right now, so I'll walk out the door. If you don't like me I won't be here forever. If you don't like this government it won't last forever. But if you leave the UK that will be forever."
Cameron's trip was a last-ditch effort to try to persuade Scotland's many undecided voters to reject independence. Up to 500,000 people out of more than 4 million registered voters are estimated to be unsure how they will vote.
Campaigning in Scotland is fraught with difficulty for Cameron, whose right-leaning party is unpopular with Scots who have traditionally voted for the left-leaning opposition Labor party and harbor bitter memories of former Conservative prime minister Margaret Thatcher's 1979-1990 stint in power.
Cameron's Conservatives have only one of 59 British parliamentary seats in Scotland, and the pro-independence Scottish National Party (SNP) has elbowed Labor aside in recent years to emerge as the dominant political force.
Cameron, his voice at times faltering with emotion, spoke after a video was shown extolling British achievements and some of the most prominent figures of British history from Winston Churchill to Alexander Fleming, a Scot who discovered penicillin.
"Independence would not be a trial separation. It would be a painful divorce," Cameron said, standing in front of a giant Union 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 privileged Englishman with aristocratic roots does not make him the best person to advocate against Scottish independence.
Scottish nationalists criticized him for staying away in the early months leading up to the vote as complacent, and now that he is showing his face, they portray him as a condescending Englishman in no position to advise Scots on how to vote.
Details of his visits north of the English border are not revealed until the last minute for security reasons and critics say his advisers try to minimize his contact with the public to avoid nationalist heckling. The visit was expected to last only hours.
CONFIDENT PRO-INDEPENDENCE LEADER
Alex Salmond, the pro-independence SNP leader, was out campaigning too on Monday in Edinburgh where he met business leaders who back the breakaway campaign.
He predicted Scotland would vote for independence and that the next time Cameron visited would be to discuss the details of the 5-million strong population's divorce settlement from the United Kingdom.
"The next time he comes to Scotland it will not be to love-bomb or engage in desperate last-minute scaremongering," Salmond said in a statement. "It will be to engage in serious post-referendum talks."
Independence supporters say it is time for Scotland to choose its own leaders and rule itself, free of control from London 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 a larger, more influential entity while enjoying an ever-increasing measure of autonomy.
"No" campaigners counter that Scotland is more secure and prosperous as part of the United Kingdom and say the end of the union would destroy three centuries of bonds and shared history as well as bring in economic and financial hardship.
Cameron's visit comes after David Beckham, the retired footballer, added his name to a petition of English celebrities who say they want the Scots to stay.
The celebrity group, "Let's Stay Together", is organizing a public rally on Monday evening in London's Trafalgar Square.
It was the pro-independence camp's turn on Sunday night when a host of Scottish rock stars including the band Franz Ferdinand and Mogwai played a concert in Edinburgh.
Singer Amy McDonald told the audience: "People fight and die for this (independence) and all we have to do is put a little cross 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 favor of maintaining the union had a lead of between 2 and 8 percentage points. But an ICM poll conducted over the Internet showed supporters of independence in the lead with 54 percent and unionists on 46 percent.
More than 4 million Scots as well as English and foreign residents, from the Highlands and Islands to Glasgow's gritty inner city estates, are eligible to vote.
The question on the ballot paper will ask simply: "Should Scotland be an independent country?" (Additional reporting by Alistair Smout and Angus MacSwan in Edinburgh and Sarah Young, William James and Kate Holton in London; Editing by Sonya Hepinstall)