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* London pledges Scotland health spending powers
* Nationalist response: Scots are not daft; why not before?
* PM Cameron warns a breakaway vote would be irreversible
* Salmond: Scotland's future should be in Scotland's hands
* Opinion polls expected on final day of campaigning (Adds nationalists response and Gordon Brown comments)
By Guy Faulconbridge and Alistair Smout
EDINBURGH, Sept 16 (Reuters) - Britain promised to guaranteeScotland high levels of state funding, granting Scots greatercontrol over healthcare spending in a last-ditch attempt toshore up support for the United Kingdom before Thursday's voteon independence.
With polls showing the decision on the fate of the UnitedKingdom is too close to call, welfare spending and the future ofthe revered National Health System have formed a central part ofnationalist Alex Salmond's case for secession.
In a deal brokered by former Labour Prime Minister GordonBrown, the leaders of Britain's three main political partiessaid they would retain the funding equation that sustains ahigher level of public spending north of the border.
"People want to see change," said the agreement, publishedin Scotland's Daily Record newspaper and signed by PrimeMinister David Cameron, Labour leader Ed Miliband and LiberalDemocrat leader Nick Clegg.
"A no vote will deliver faster, safer and better change thanseparation," the agreement said.
Cameron, whose job is on the line if Scots vote to break theUnited Kingdom, warned on his last visit to Scotland beforeThursday's vote that there would be no going back and that anyseparation could be painful.
British leaders accept that even if Scotland votes to keepthe 307-year union, the United Kingdom's structure will have tochange as the rush to grant so many powers to Scotland willprovoke calls for a less centralised state from voters inEngland, Wales and Northern Ireland.
Swathes of voters in the former industrial heartlands ofnorthern England and Wales depend on state welfare spendingwhile some English lawmakers in Cameron's own party have askedalready asked for England to be given more powers.
BIGGEST THREAT
In the face of the biggest internal threat to the UnitedKingdom since Ireland broke away nearly a century ago, Britain'sestablishment - from Cameron and the City of London to soccerstar David Beckham - have united in an almost panicked effort toimplore Scots that the United Kingdom is "Better Together".
"There's no going back from this. No re-run. If Scotlandvotes 'yes' the UK will split and we will go our separate waysforever," Cameron, his voice at times faltering with emotion,said 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."
The visit by Cameron, who is also grappling with what to doabout Islamist militants in Syria and Iraq, drew a swiftrebuttal from nationalist leader Salmond who argued Scotland hada historic opportunity to rule its own affairs.
"The next time he comes to Scotland it will not be tolove-bomb or engage in desperate last-minute scaremongering -and following a Yes vote it will be to engage in seriouspost-referendum talks," the 59-year-old Scottish leader said.
If Scots vote for independence, Britain and Scotland wouldface 18 months of negotiations over everything from North Seaoil and the pound to European Union membership and Britain'smain nuclear submarine base.
The prospect of breaking up the United Kingdom, the world'ssixth largest economy and a veto-wielding permanent member ofthe United Nations Security Council, has prompted citizens andallies alike to ponder what would be left.
The White House said it would prefer the United Kingdom toremain "strong, robust and united" while Martin Amis, one ofBritain's best-known novelists, said secession would be a leapin the dark.
"What would be left of it if Scotland got out is a verydiminished country," said Amis, whose novels have explored thedarker side of British life.
Sterling has fallen on the risk of a secession vote butprices for Britain's currency, bonds and stocks indicateinvestors are not yet pricing in a vote for independence.
YES OR NO?
Aside from the finance and geopolitics of a secession vote, on the streets of Scotland the battle for voters was reachingits peak before the last full day of campaigning on Wednesday,when several opinion polls are due to be released.
Voters will be asked on Thursday to answer Yes or No to thequestion "Should Scotland be an independent country?".
Brown pressed the unionist case in a speech to Laboursupporters in Clydebank, once home to much of Scotland'sshipbuilding industry.
"I yield to noone in my patriotic pride in being Scottish,"Brown said. "The effect on September 18 if you vote 'Yes' is toend every single last remaining link that exists, theconnections that we have with our friends, neighbours andrelatives."
The Glasgow-based Herald newspaper on Tuesday came out infavour of Scotland staying within the United Kingdom but saidgreater autonomy must follow.
It rejected the notion that an independent Scotland would bea disaster and said that the current set-up did not meetScotland's needs and aspirations.
But on the Isle of Lewis there was support for Scotlandrunning its own affairs.
"Very simply I want the people of Scotland to make decisionsfor Scotland," said Margaret Ann MacLeod, 46, a dentalhygienist, in the island's main town Stornoway.
Seeking to tap into a cocktail of historical rivalry,opposing political tastes, and a perception that London hasmismanaged Scotland for decades, nationalists say an independentScotland could build a wealthier and fairer country.
Unionists say independence would needlessly break up theUnited Kingdom and usher in years of financial, economic andpolitical uncertainty. They have warned that Scotland would notkeep the pound as part of a formal currency union.
The debate raged on the streets and in the media.
Hugh Reilly, in a column in the Scotsman, evoked the 1314Battle of Bannockburn, when Robert the Bruce defeated England'sKing Edward, to whip up sentiment for a "Yes" vote.
"A Scots army, this time made up of voters, has a date withdestiny," he wrote.
He also quoted national poet Robert Burns, who had describedthose who signed the 1707 Act of Union as a "parcel of rogues".
"On Thursday Scots have a once in a lifetime chance to end300 years of being a junior partner in the artificial countryknown as Britain," Reilly wrote.
But in the same newspaper, Peter Jones accused Salmond of"crude, faith-based nationalism". He said Salmond had run "themost dishonest, deceiving and duplicitous campaign I have everknown in politics". (Additional reporting by Angus MacSwan and by CathalMacNaughton of the Isle of Lewis; editing by Janet McBride)
