By Andrew Osborn
LONDON (Reuters) - Britain's national security could be weakened if Scotland votes to leave the United Kingdom next year, the British government said on Tuesday.
An independent Scotland would also be less able to protect itself, a government report said.
The intervention, part of the government's campaign to keep Scotland inside the United Kingdom, feeds into an emotive debate which Britain's three main parties think they are winning.
Opinion polls suggest only a third of Scots back independence ahead of a vote on September 18, 2014.
Prime Minister David Cameron's ruling two-party coalition and the opposition Labour party strongly oppose Scottish independence and fear a "Yes" vote could dilute Britain's global clout and imperil its Scotland-based nuclear deterrent.
The report said it would take an independent Scotland a long time to build up its own security infrastructure and that would directly affect the security of what was left of the United Kingdom. It was also have only a fraction of Britain's security budget at its disposal to do so.
"In the meantime the risk would be of security levels diminishing to the detriment of both Scotland and the continuing UK," said the report, presented by Home Secretary (interior minister) Theresa May in the Scottish capital, Edinburgh.
Without proper planning and investment, an independent Scotland would also be less able to protect Scotland against threats from everything from international terrorism to cyber attacks, it said, saying such a situation would "result in an increased risk to the Scottish people."
The "Yes Scotland" campaign, led by the Scottish National Party (SNP), wants independence to be a reality by 2016 after next year's referendum.
It has tried to tap into an emotive cocktail of historical rivalry, opposing political tastes, and a perception that the British parliament in London does not nurture Scotland's interests, but has so far struggled to boost its support.
The SNP has argued that its pledge to remove Britain's submarine-based nuclear arsenal from Scotland in the event of a "Yes" vote and its determination to ensure Scottish troops no longer take part in what it calls "illegal wars" would make it less of a target for terror attacks.
But the report flatly rejected that contention, saying an independent Scotland would still face a wide range of risks.
Nor would an independent Scotland be able to rely on Britain's various intelligence and security agencies, the report said, saying it would have to create its own from scratch.
Financially, it would be tough for Scotland to buy itself such a capability, the report said, saying the nationalists' proposed annual budget for defense and security of 2.5 billion pounds was 14 times smaller than Britain's current budget.
An independent Scotland would not be able to automatically receive shared intelligence from Britain's allies either.
Christine Grahame, an SNP lawmaker in Scotland's devolved parliament, poured scorn on the report, saying its contents were "the same old tired and discredited nonsense".
"This is 'Project Fear' at its worst - trying to politicize issues of security and anti-terrorism in this way is the height of irresponsibility," she said.
(Editing by Angus MacSwan)