DAVID CAMERON'S Government believes it has already won the battle over Scottish independence 14 months before the referendum.

Senior Coalition sources claim the only question left is how small the Yes vote will be on September 18, 2014.

They claim any narrowing of the polls between now and then will be because of "protest votes", not any genuine increase in support for Scotland leaving the UK.

The comments will be met by derision from the SNP, Yes Scotland and the Scottish Government, who insist there is still a long way to go before the argument is settled.

SNP First Minister Alex Salmond recently said the current debate was the "phoney war" before the campaign proper began.

Sources predict the Yes vote could be boosted by those who want to register anger at the Conservative-Liberal Democrat Coalition or at Labour, which is leading the Better Together campaign.

They stressed the UK Government must guard against such a protest by ensuring voters do not feel the only way to get more devolution is to vote Yes.

A senior source close to the Prime Minister made clear the Coalition believed the chance of independence no longer existed. "We have won the argument on independence," declared a Government minister.

"Ordinary people on the doorsteps have made their mind up about this issue. But they may vote Yes next September for other reasons. We are now fighting to ensure we've got a big enough majority to determine what happens after the referendum."

Asked if he meant the settled will of the Scottish people was against independence, and pro-UK forces wanted as big a win as possible to stop the SNP resurrecting their campaign after 2014, he replied: "Yes, I think that's right."

The remarks go further than those of Mr Cameron, who recently goaded the SNP by insisting the Coalition was winning all the arguments on independence and, referring to the referendum, urged the First Minister and his colleagues to "bring it on".

Coalition insiders put a key threshold for the Yes vote at 40% – above which they believe the SNP would be able to argue relatively quickly for another referendum, creating a so-called "neverendum".

Whitehall insiders compared Westminster's approach to Holyrood's to "professionals versus amateurs", but last week Downing Street was forced to disown claims the Ministry of Defence is looking at ways to keep nuclear weapons in Scotland even if Scots vote to leave the UK.

A day earlier No 10 admitted plans for a voting system in the House of Commons in which Scots MPs would be barred from voting on English-only issues would be published before the independence referendum.