LONDON, April 30 (Reuters) - The UK Treasury escalated its attack against Scottish independence on Wednesday, dismissing estimates of North Sea oil revenue as too optimistic and promising to lay out the fiscal benefits of staying in the United Kingdom in coming weeks.
In a speech in Edinburgh, the Treasury's Chief Secretary Danny Alexander accused the ruling Scottish National Party (SNP) of peddling "myth after myth" on future state finances to win support at an independence referendum on September 18.
Anti-independence campaigners have stepped up their fight as opinion polls show support for independence gaining ground although nationalists are still behind the unionists.
Alexander said Scotland's 5.3 million people needed to realise that the SNP-dominated Scottish government was promising public spending and tax revenues that it could not deliver if it were to sever its 307-year-old tie with England.
"The nationalists' assertions on Scotland's finances are at best ill-informed and at worst, deeply misleading to Scottish voters," he told a group of business leaders.
His speech came as new oil data was released which Alexander said showed total UK North Sea revenues last year were 4.7 billion pounds, less than the Scottish government estimated in its financial plan for independence.
He said over the past two years, revenue coming from oil for the United Kingdom had been more than 3 billion pounds lower than the Scottish government's "most cautious" forecasts.
The Scottish government's White Paper on the case for independence released last November put revenue at about 48 billion pounds in the five years between 2012/13 and 2017/18.
"It leaves tens of billions of pounds missing ... that, under independence, can't be raised across the UK but will have to be raised from Scottish businesses and individuals or cut from Scottish services," Alexander said.
"While we should celebrate that our human resources have such potential, we need to be realistic when it comes to our natural resources," added the Liberal Democrat MP for the Highlands.
Alexander also questioned whether an independent Scotland would be able to bail out banks that ran into trouble, given the size of the large financial sector north of the border.
He called Scottish First Minister Alex Salmond "belligerent" by insisting Scotland would strike a deal to continue using the pound after any "Yes" vote even though the main UK parties have ruled this out.
But Scottish Finance Secretary John Swinney dismissed Alexander's speech as "desperate" and typical of a negative campaign run by unionists that was trying to frighten people into voting "No" to independence but having the opposite effect.
He said investment in the North Sea was at record levels and that the industry had a great future for many decades to come with oil a bonus, not the basis of Scotland's economy.
Swinney said the UK Treasury should tell the public about the assets that would go to Scotland if there was a Yes vote.
"As part its campaign rhetoric we know the UK government talks about Scotland's share of the debt run up by successive Westminster chancellors," he said in a statement.
"It cannot be taken seriously if it does not also talk about Scotland's share of assets."