Before the Scottish Independence referendum U.K. leaders make their last calls for unity. On his last visit to Scotland before Thursday's referendum, British Prime Minister David Cameron, in an emotional speech, warned Scotland of the costs of independence while promising to do more for the country if the "No" vote succeeds.Cameron, along with Labour leader Ed Miliband and Liberal Democrat leader Nick Clegg, on Tuesday promised to extend new powers to the Scottish parliament if Scotland refused independence. Cameron attempted an emotional speech in the Scottish city of Aberdeen as part of his "Better Together" campaign. In his speech, the prime minister warned that a "Yes" vote would deprive the Scottish people of a shared currency and pooled pension arrangements. "There's no going back from this. This is a once-and-for-all decision. If Scotland votes 'Yes', the U.K. will split, and we will go our separate ways forever." He warned Scottish citizens against an independence decision: "Head and heart and soul, we want you to stay. Please don't mix up the temporary and the permanent. Please don't think: 'I'm frustrated with politics right now, so I'll walk out the door and never come back.' 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 U.K. - that will be forever," he said.The declaration of the three U.K. party leaders, under the headline "The Vow" on the front page of the Daily Record newspaper, has pledged to devolve new powers to an autonomous Scottish parliament.Payments for national health service will be decided by the Scottish Parliament and the U.K. will ensure equal distribution of resources and security, according to the declaration. The opposition party's leader Ed Miliband said he believed the "Yes" campaign had delivered a clear message to U.K. parties that change was needed. "The will of the people of Scotland for economic and political change has been heard and we will deliver. I ask the people of Scotland to lead that change of our whole British constitution," instead of a "a future of separation and risk" offered by an irreversible "Yes" vote.The Pro-independence bloc was skeptical about the statements. Blair Jenkins, chief executive of Yes Scotland, said Cameron's speech "was the same litany of empty threats and empty promises we have come to expect from the "No" campaign - and he is the prime minister who has been orchestrating the campaign of ridiculous scaremongering being directed against Scotland."If Scotland votes for independence in the referendum on Thursday, Sept. 18, a 307-year-old union will be broken. Opinion polls showed varied results at around 53 percent for "No" to Scotland leaving the U.K., to 54 percent for "Yes." The number of undecided voters has been put at around 500,000, among 4.2 million registered voters.If the "Yes" vote is successful, Scotland will leave the U.K. on proposed a Independence Day of March 26, 2016 following the negotiations between London and Edinburgh governments.