DAVID Cameron has emphatically ruled out a deal with the SNP to deliver the Nationalists' demand for full fiscal autonomy.

The Prime Minister said the plan, which would see the Scottish Government assume responsibility for almost all tax and spending decisions north of the Border, would end a key feature of the UK, the "fiscal union" which allows taxes to be shared and resources transferred between nations.

He launched a passionate defence of the Union after he was accused of preparing a "grubby deal" with the SNP.

Ahead of the Prime Minister's visit to Glasgow yesterday, Labour had claimed the Conservatives were moving towards fiscal autonomy for England, paving the way for a possible agreement on the issue with the Nationalists.

But speaking at the city's Emirates Arena, where he launched the Scots Tories' manifesto, he said: "I don't want full fiscal autonomy.

"I'm a true believer in the United Kingdom.

"When I said it would have broken my heart if Scotland had voted to leave the UK, I absolutely meant it."

He said the UK was not just a "place on the map" or a "shared history," adding: "It is also solidarity and that is what the fiscal union is about.

"If parts of Scotland have a difficult year, the rest of the UK is there for you to help.

"If parts of England have a difficult time, parts of Scotland are there to help."

Referring to the Institute for Fiscal Studies' warning that a fiscally autonomous Scotland would be £7.6billion worse off this year, he told supporters: "I think it would be bad for Scotland, as the IFS figures demonstrate, but it would be bad for the country I love, and that country is called the United Kingdom.

"It is a solidarity union as well as a union of nations, and let's not forget that here in the Conservative Party."

Nicola Sturgeon, the SNP leader, has said her MPs will press for full fiscal autonomy in the next parliament.

She argues the set-up would take a number of years to introduce.

Mr Cameron said the prospect of a Labour wipe-out in Scotland, as the party faces heavy losses to the SNP, meant he was the only leader with a chance of heading a majority government after May 7.

He claimed the alternative was the "terrible prospect" of a minority Labour government supported by the SNP.

Warning of a "coalition of chaos," he said: "Ed Miliband cannot become prime minister without SNP support.

"That has a consequence for Scotland and it has a consequence for the rest of the United Kingdom.

"It is the appalling prospect of having a Labour prime minister propped up by a group of people who don't want to be in that parliament, don't want to be in that country, and would like to see the whole thing break up - and in the meantime are going to push for an economy-wrecking borrowing, taxing and spending agenda."

Mr Cameron styled the Conservatives "the party of real devolution".

He repeated his promise to devolve further tax and welfare powers to Holyrood but said that would be balanced by blocking Scots MPs from voting on income tax rates south of the Border.

The Prime Minister also highlighted promises to increase support for military families and veterans.

Margaret Curran, Labour's shadow Scottish Secretary, said: "Scotland is now in danger of being caught in a classic pincer movement between a Tory party that wants to cut Scotland out of the UK budget and the SNP that wants to cut Scotland out of UK taxes.

"We now have a Tory party committed to an England only tax system and the SNP hell bent on Scotland only taxes."

SNP deputy leader Stewart Hosie said: "Electing a strong team of SNP MPs will let Scotland lock David Cameron out of Downing Street and ensure that Scotland's voice cannot be ignored at Westminster."