Nicola Sturgeon
SNP leader Nicola Sturgeon took part in a leaders' debate on STVGetty

Nicola Sturgeon has failed to rule out a pledge to hold another referendum on Scotland's independence from the rest of the UK, prompting boos and jeers as the SNP leader debated live on TV.

The first minister was asked about her party's plans for next year's Scottish Parliament election when she took part in STV's leaders' debate.

"I do [still believe in independence]. But I respect the outcome of the election. This Westminster election is not a rerun of the referendum," Sturgeon said.

The audience member pushed the SNP leader on the issue and asked what she had planned for the 2016 election. "That's another matter," Sturgeon replied.

The first minister went onto to stress that she wanted to do a deal with Ed Miliband and Labour in Westminster to keep the Tories from returning to power.

"Nicola, we don't need your help. What we need is people north and south of the border, people in Scotland, people in England and people in across Wales coming together to kick out an out of touch government," said Jim Murphy, the leader of Scottish Labour.

Murphy, a former Labour front bencher, argued that only his party could beat the Tories and curb their spending cut plans.

"Only Labour is big enough, only Labour is strong enough to beat the Tories and their austerity," he declared.

The Conservatives seized on Sturgeon's comments and claimed the nationalist was planning to "hold Great Britain to ransom".

'Tonight Nicola Sturgeon has promised that she'd prop up a minority Labour government – and hold Great Britain to ransom, vote by vote, policy by policy," said Grant Shapps, the chairman of the Tories.

"And that means more debt, higher taxes and the end of Trident – wreaking havoc on our economy and putting the security of British people and their families at risk.

"Weak Miliband doesn't stand a chance. He's in the pocket of Alex Salmond and Sturgeon: and you'll pay the price."

The latest poll from YouGov, which surveyed more than 1,600 people between 6 and 7 April, put Tories two point ahead of Labour (35% vs 33%), with Ukip on 14%, the Liberal Democrats on 8% and the Greens on 5%.

But north of the border the SNP are well ahead of Labour, with a YouGov poll putting Sturgeon's party 17 points ahead of Scottish Labour (46% vs 29%).