Current proposals for televised debates in the build-up to the general election are "unacceptable", Nicola Sturgeon has said

Scotland's first minister-in-waiting is demanding that broadcasters think again on their proposals and said "it would be a failure in your duty of impartiality" if the debates go ahead as currently planned.

Ms Sturgeon was speaking to an audience of supporters in Dumfries in the second of a series of events she is staging around the country to set out how she will lead Scotland and the SNP when she succeeds Alex Salmond next month.

The BBC, ITV, Sky and Channel 4 have announced plans to hold three debates.

One is to feature Ukip leader Nigel Farage, David Cameron, Ed Miliband and Nick Clegg, another with only a head-to-head debate between the Conservative and Labour leaders, and one with them and the Liberal Democrat leader.

The SNP is now the third-largest party in the UK with more than 83,000 members and has been joined by the Green Party and Plaid Cymru in its criticism of the TV proposals.

Speaking in Dumfries, Ms Sturgeon said: "We are - without doubt - Scotland's party of social democracy. The party of aspiration and opportunity.

"The party that knows that a strong economy and a fair society must go hand-in-hand if everyone in our country is to get a decent chance in life.

"And, crucially, a party with the freedom of thought and action to fashion a policy programme to support that vision.

"Which makes it all the more remarkable, does it not, that any broadcaster would even think about excluding us from general election TV debates?

"I want to send a direct message to the BBC, ITV, Sky and Channel 4: To exclude not just the SNP, but also the Greens and Plaid Cymru, would be to wilfully ignore the reality of the political landscape that exists, not just in Scotland, but across the UK.

"It would be a failure in your duty of impartiality.

"If you didn't realise already that your proposals are unacceptable - not just to us, but to every democrat in our land - then surely yesterday's opinion polls puts the matter beyond any doubt. It is time to think again.

"Be in no doubt - in the general election, the SNP will be seen and Scotland's voice will be heard."

Yesterday, an Ipsos MORI poll for STV News found that 52% of Scots would vote for the SNP if there was a Westminster election tomorrow, suggesting the party could secure 54 Scottish seats in the Commons, with Labour reduced from 40 to four.

Meanwhile, a YouGov poll for The Times put the SNP on 43%, which would give them 47 seats.

When the TV debate plans were announced earlier this month, a BBC Scotland spokesman said: "In Scotland, the BBC is proposing a debate, in peak time on BBC One, involving the leaders of the SNP, Scottish Labour, Scottish Conservative and Scottish Liberal Democrat parties.

"We have written to the parties to begin discussions about our proposals and we will ensure impartiality during the election in Scotland.

"Full details of our content will be released over the coming months once they are finalised."

The SNP has not ruled out taking legal action over the plans to exclude them from the UK-wide live TV debates.

A BBC spokesman said: "The BBC, along with other broadcasters, has put forward a proposal for UK-wide debates and an invitation to party leaders to discuss its own broader plans for debates across the UK, including in Scotland.

"We make editorial judgements about coverage during the general election campaign informed by evidence of past and current electoral support.

"Opinion polls are part of that evidence whereby we take account of consistent and robust trends across different polls over time, rather than reacting to individual polls.

"We have also said that we will continue to look at any further evidence of changes in electoral support as we get closer to the election campaign.

"The BBC Trust will be launching a public consultation on the relevant guidelines next week."