London: British Prime Minister David Cameron on Wednesday promised he wouldn’t increase value added tax if re-elected in May after being challenged to rule out such a move by the opposition Labour Party.

“The answer is yes,” said Cameron when asked to pledge he wouldn’t raise the consumption tax, which is currently set at a standard rate of 20 per cent. “I ruled out an increase.” Miliband said nobody would believe Cameron’s promise ahead of a tight national election on May 7 and that it was time for a Labour government.

Meanwhile, Alex Salmond, the former Scottish National Party leader, has vowed to stop David Cameron forming a minority Conservative government in a hung parliament by voting down a Tory Queen’s Speech.

Salmond’s comments are intended to reassure former Labour supporters in Scotland that voting SNP on May 7 will not allow Cameron to enter Downing Street “through the back door”.

It further highlights the key role Salmond could play as a kingmaker in a hung parliament, possibly putting him in a position where he could install Ed Miliband in Number 10, even if Labour finish second in the election.

Salmond said that if the SNP joined forces with Labour MPs in the Commons they could vote down a Queen’s Speech brought forward by a minority Tory government, ensuring Cameron was “locked out”.

The Conservatives accused him of “trying to sabotage the democratic will of the British people” while Labour called his balance of power prediction “bluster and bluff”.

The SNP currently has six MPs at Westminster but opinion polls suggest the party could trounce Labour in Scotland, possibly winning more than 50 of the 59 seats north of the border.

Salmond has made it clear repeatedly that he would not prop up a Tory government but that some kind of deal with Labour is possible. Ed Miliband has ruled out a formal Labour/SNP coalition, but not a looser arrangement.

If Cameron does emerge as leader of the largest party — but short of a Commons majority — he may need to do a deal with the Liberal Democrats, Democratic Ulster Unionists and even Ukip MPs to secure power.

Under that scenario, if he was unable to secure the passage of his Queen’s Speech Cameron would be required to let Miliband have a go at forming a government.

The Labour leader would then have to make a judgement on whether Labour could legitimately govern, having finished second in the election and relying on the support of the SNP, a party which wants to break up the United Kingdom.