Alex Salmond has suggested he could act as kingmaker - and possibly Deputy Prime Minister - in the event of another hung parliament at Westminster.

The SNP leader, who has added to ­speculation that his career lies at Westminister, declined to rule out a coalition with Labour after the 2015 General Election, though he said such a move would be unlikely.

Instead, the party could keep Ed ­Miliband in Downing Street by offering support on votes on a case-by-case basis, he said.

His comments follow a poll last week that suggested the SNP would take most of Labour's seats in Scotland if the election were held tomorrow.

One calculation forecast the number of Scottish Labour MPs would collapse from 40 to just four, while the SNP would go from six to 54 MPs.

Mr Salmond again suggested that he could be among their number, saying he was considering standing for Westminster next May.

At Westminster his party would never enter a coalition with the Conservatives, the First Minister insisted. He is working on a ­"diary-style" book to be published early next year.

He suggested Labour would pay the price for a generation for cam­paigning alongside the Tories on independence.

Opinion polls suggest 2015's General Election could be an extremely close-run contest between Labour and the Conservatives for the keys to No 10.

Although Labour lead in most surveys, they trail the Conservatives on trust over the economy.

Asked about possible coalitions, Mr Salmond said the SNP would never do a deal with the Conservatives at Westminster. But he refused to rule out possibly forming a coalition government with Labour, although he suggested that would not be possible with Mr Miliband in charge.

During talks with Labour in 2010, the LibDems insisted that Gordon Brown had to stand aside as the price of their support. Nick Clegg also successfully negotiated the position of Deputy Prime Minister to represent the smaller party in the coalition.

"Parties change their leaders sometimes, so we might get a different direction," Mr Salmond said, "but I think that it's unlikely that the SNP would see itself in a Westminster coalition."

He suggested, however, that the SNP could negotiate deals in return for its backing on certain votes. If Labour governed as a minority administration there would be greater tractions on negotiating support on a case-by-case basis, he said.

As the former leader of a minority administration himself, he suggested that he was well-placed to understand the negotiations that go into such arrangements.

The First Minister, who served as an MP between 1987 and 2010, also confirmed that he was still weighing up a possible Westminster comeback.

"I am going to make up my mind in a few weeks," he said. "I intend to continue to represent the people of the north-east of Scotland if they wish to elect me." Mr Salmond also reiterated his belief that Scotland would eventually be independent.

In a separate interview, Deputy First Minister Nicola Sturgeon, who will take over from Mr Salmond later this month, said there could be no shortcuts and the only way to independence was through another referendum.

Labour sources rejected the First Minister's claim that last week's poll showed voters were angry Labour campaigned with the Tories. Labour also accused the SNP leader of leaving office with a trail of broken promises behind him, on issues such as student debt and healthcare, a charge also echoed by the Conservatives.