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* Sterling, shares and bonds fall; banks brace for Scotlandvote
* Britain scrambles to offer more powers to Scots
* Unionist campaign criticised as negative and complacent
* Nationalists claim momentum ahead of Sept. 18 vote (Adds Gordon Brown comments)
By Guy Faulconbridge and Angus MacSwan
LONDON/EDINBURGH, Sept 8 (Reuters) - British financialmarkets tumbled on Monday after an opinion poll showed for thefirst time this year that Scots may vote for independence in areferendum next week, breaking up the United Kingdom.
The survey prompted concern bordering on panic amongBritain's ruling elite, with Prime Minister David Cameron'sConservative-led government promising proposals this week togrant Scotland greater autonomy if it stays.
Cameron's job would be on the line if Scots vote on Sept. 18to secede, less than eight months before a national electionplanned for May. His spokesman said on Monday the government wasnot making contingency plans for the possibility of Scottishindependence.
Sterling fell more than 1 percent - its biggest one-day dropin 13 months - to $1.6141, long-dated government bondstumbled and 3.5 billion pounds ($5.7 billion) was wiped off themarket value of six London-listed companies with large exposureto Scotland.
"Be afraid, be very afraid," Deutsche Bank analysts said inone of a flurry of notes by banks to investors outlining therisks to the U.K. economy and European unity of Scottishindependence.
Unionists played down the market moves. Alistair Darling, aformer finance minister who leads the unionist 'Better Together'campaign said it was natural in the run-up to a vote. "For aslong as there's uncertainty, you will get a bit of jitterinessin the system," he told reporters in Edinburgh.
After months of polls showing nationalists heading fordefeat, the survey by the YouGov pollster raised the realprospect that secessionists could achieve their goal of breakingthe 307-year-old union with England.
Polls indicate Scots have been irked by a perceived scarecampaign by unionists while pro-independence Scottish FirstMinister Alex Salmond appeared stronger than Darling in atelevision debate on Aug 25. The next poll, a TNS opinion surveyon Scotland is due to be published at 2301 GMT.
If Scotland voted to leave the United Kingdom, Cameron wouldface calls to quit before the general election, while theopposition Labour party's chances of gaining a majority could bescuppered if it lost its 40 Scottish lawmakers.
Cameron, who visited Queen Elizabeth in Scotland on Sunday,has insisted he will not resign. British media quoted a palacesource as saying the monarch was concerned and had asked fordaily updates on the situation.
A vote for independence by Scotland's 4 million voters wouldbe followed by negotiations with London on what to do about thepound, the $2.1 trillion national debt, North Sea oil and thefuture of Britain's nuclear submarine base in Scotland ahead ofindependence pencilled in for March 24, 2016.
With less than two weeks to go before the Sept. 18 vote, thepoll put the "Yes" to independence campaign on 51 percentagainst "no" camp on 49 percent, excluding undecided voters,overturning a 22-point lead for the unionist campaign in just amonth, the Sunday Times said.
BETTER TOGETHER?
Less than 12 hours after the poll was released, Britain'ssecond most powerful man promised that plans would be set out togive Scotland more autonomy on tax, spending and welfare ifScots vote against independence.
"You will see in the next few days a plan of action to givemore powers to Scotland," finance minister George Osborne said.
It was unclear if Osborne was promising additional powers ora discussion of devolution that Britain's political parties havelong been offering Scotland if it votes to stay in the union.
But the comments were cast as panic by Scottish FirstMinister Alex Salmond, leader of the Scottish National Party(SNP), who said the campaign to save the union was spirallinginto self-destruction.
He scoffed at last-minute offers of greater autonomy forScotland from London parties, saying: "I've no doubt they'llcobble together something because having failed to scare theScottish people, the next step is to try to bribe us."
Former British Prime Minister Gordon Brown, speaking for the"No" campaign in a miners' welfare club in central Midlothian onMonday evening, outlined a timetable for the devolution offurther powers to the Scottish Parliament.
Brown, a Scot and Labour MP, said discussions over furtherpowers would begin the day after a "No" vote, with legislationput before the U.K. parliament by January 2015
It would strengthen the Scottish Parliament, giving it more power over welfare, finance, social and economic policy, hesaid.
"This moves us as close to federalism as we can," he said.
"Scotland is already a nation. We are proud of our history and culture. Do we want to sever all constitutional links withour friends, our neighbours, our relatives in England, Wales andNorthern Ireland?"
UNIONISTS
The unionist campaign has also drawn criticism from manyunionists who say it has been complacent, negative and riven bydivisions.
"The campaign so far has been narrow and negative," saidHenry McLeish, a former Scottish first minister from the Labourparty. "It's also been patronising and its really lackedemotion, lacked passion and lacked soul so therefore in acountry like Scotland where the heart and head are to be takentogether, that's been a major deficiency."
The apparent surge in support for independence could alarmunionists and thus push more people out to vote. The last surveyto show backing for independence was a Panelbase pollcommissioned by the Scottish National Party in August 2013 thatput it at 44 percent versus 43 percent and 13 percent undecided.
People close to Cameron say he does not want to go down inhistory as the prime minister who lost Scotland. But he hasconceded that his privileged background and centre-rightpolitics mean he is not the best person to win over Scots,usually more left-wing than the English.
That has left the opposition Labour party with much of theburden of trying to convince Scots not to break the union.
KNIFE EDGE
British newspapers headlined the biggest domestic threat tothe United Kingdom since Irish nationalists created a breakawayrepublic almost a century ago.
"Scots vote chaos - Jocky Horror show," read the front pageof the Sun, Britain's most read daily, while the right-wingDaily Telegraph declared on "Ten days to save the Union".
In Scotland, the pro-union Scotsman cautioned against apanic reaction and some investors said the sell-off overScottish independence fears was overdone.
"A strong bounce in sterling is likely on a 'No' vote, whichis still very much the most likely outcome," said TrevorGreetham, a fund manager at Fidelity. "In the event of a 'Yes',things would get messier."
The FTSE 100 Index of blue chip companies fell asmuch as 1.2 percent, dragged down by Babcock, LloydsBank, Royal Bank of Scotland, Standard Life, energy group SSE and Weir group.
The cost of insuring against default by banks withsignificant Scottish exposure, such as Lloyds and RBS, rose. Theso-called credit default swap on 82 percent state-owned RBS had the second biggest daily rise this year,according to Markit prices.
Banking industry sources told Reuters last week that Lloydsis considering moving its registered offices to London if Scotsvote for independence. RBS is also examining its options.
The two banks have warned that an independent Scotland wouldpresent a significant risk to their businesses, impacting theirfunding, tax and compliance costs.
Nationalists accuse London of squandering Scottish wealthand say that Scotland would be one of the world's richestcountries if it took control of its own destiny.
Unionists, including Britain's three main political parties,say the United Kingdom is stronger if it stays together and thatScottish independence would bring significant financial,economic and political uncertainty.(1 US dollar = 0.6187 British pound) (Additional reporting by Sarah Young, Andy Bruce, Kate Holton,Kylie MacLellan, Patrick Graham, Jamie McGeever, Matt Scuffhamand Atul Prakash; Editing by Tom Heneghan)
