The SNP would hold "the power" if a Labour government needed its votes to survive, Alex Salmond has insisted.

The former first minister said the party would demand the scrapping of Trident as the price of entering a "confidence and supply" agreement with Ed Miliband.

But he said the "more likely" situation would be Labour and the SNP working together on a vote-by-vote basis - including detailed negotiations about Budget packages.

The comments, in a round of broadcast interviews, were immediately seized on by the Tories, with defence minister Anna Soubry branding them "terrifying".

Mr Salmond, who is standing to re-enter parliament in the Gordon constituency, told the BBC's Andrew Marr Show it would be "very good for Scotland" if there was a decisive number of SNP MPs after May 7.

"If you hold the balance, then you hold the power," he said.

Asked if that meant Ed Balls or another Labour chancellor would have to negotiate their Budget with the SNP, he replied: "Yes, any minority government has to negotiate in order to win a majority for its proposal. That is patently obvious. To deny that is to deny reality.

"If the SNP are in these circumstances it will be very good for Scotland, certainly."

Mr Salmond mooted an example where he would propose an amendment to Budget legislation in order to create a high-speed rail line to Edinburgh. "What would Ed Balls do?" he asked.

Pressed on what kind of deal was possible with Labour, Mr Salmond said: "The Labour Party have ruled out a coalition but haven't ruled out a confidence and supply arrangement, where you have a set programme ... I think it is more likely to be a vote by vote arrangement."

The former SNP leader said: "I think it's a very bad idea in politics to bend under pressure."

Mr Salmond went on: "Hopefully that decisive bloc of SNP MPs will move the Labour Party in a different direction.

"I think there is lots of people - certainly lots of people in Scotland.. but I think people across these islands are pretty fed up with the duopoly at Westminster and might want to see politics a bit more interesting, where parties have to work for their votes and have to justify things on a vote by vote basis to the people of the country.

"I think lots of people will find that a much more exciting and productive system of politics."

Mr Salmond told Pienaar's politics on BBC Radio 5 Live that Mr Miliband had been "very foolish" to rule out a formal coalition with the SNP.

The mistake was "not because it was likely to happen but because he did it under pressure from the Conservative Party".

"I think it's a very bad idea in politics to bend under pressure," he added.

Mr Salmond said he believed Scottish independence was now "near inevitable", and hinted that a commitment to a new referendum could be included in the SNP manifesto for the 2016 elections north of the border.

"The story is not finished. I think the direction is now as near inevitable as anything can be in politics," he told the Marr Show.

"I think what has happened is that we have established the gold standard of how you have a process for Scotland becoming independent.

"What you have to have is a party or parties have to put it in their manifesto for the Scottish election, they have to win a majority in that proportional parliament to hold a referendum and then the decision of course lies with the Scottish people."

Mr Salmond also appeared to rule out taking over as leader of the SNP's Westminster group in the new parliament.

"No, Angus Robertson is leader of the group at Westminster," he said.

"The SNP has a collective approach on these things but the person who calls the ultimate shots is Nicola Sturgeon."

Pushed on whether renewing Trident was a "red line" for the SNP that would prevent a deal with Labour, Mr Salmond said: "You couldn't have a coalition or a confidence and supply, but a vote by vote is what comes up in the House of Commons."

Appearing alongside the former Scottish first minister on Marr, Ms Soubry said his words were "terrifying".

"The thought that we are in a position where you can be actually controlling in the way that you have described this United Kingdom fills me with absolute horror," she said.

"The audacity is atonishing. There was a wonderful debate in Scotland, you lost it. We are a United Kingdom, that is what the people of Scotland wanted.

"Because of the inadequacies of Labour north of the border you guys are now in the position where you can be the power broker."

Scottish Labour leader Jim Murphy said the SNP would have "no bargaining chips" to control a minority government headed by Ed Miliband as they had already ruled out working with the Tories.

And he warned Scots that they could not vote SNP to get a Labour government "by proxy".

"People are coming more to the understanding that the biggest party gets to form the government," Mr Murphy told the BBC's Sunday Politics.

"It is either Labour or the Tories. You cannot vote for a Labour government by proxy ... it is one or the other."

Asked about polls suggesting Labour faces losing dozens of seats to the SNP in Scotland, Mr Murphy admitted his party had not been "good enough" over recent years.

But he argued that the public was "starting to listen" to what they had to say.

"We have got a long way to go," he said. "If these polls are repeated on election day this will be a bloody, awful showing for the Scottish Labour Party.

"But much more important it will be a dreadful day for Scotland because by accident we would re-elect David Cameron ...

"David Cameron would cling on to power. He would be an accidental prime minister."

John Lamont MSP, Scottish Conservative chief whip said: "Four weeks before postal ballots go out, Alex Salmond is taking the votes of people in Scotland for granted and planning back-room deals with Labour from a TV sofa in London. Even for him, this is stunning arrogance.

"Now he is talking up the prospect of a vote-by-vote deal with Labour - one Ed Miliband still refuses to rule out.

"That would mean the SNP holding a weak Labour Party to ransom on every vote, every day, all with the aim of trying to weaken the United Kingdom.

"A year after Scotland gave a clear and unequivocal No to the SNP's separation plans, Alex Salmond would be back at the heart of Westminster trying to sow chaos with our future."