Nicola Sturgeon has accused David Cameron of a direct breach of the post-referendum promise of more powers for Scotland with his manifesto giving English MPs the final say on income tax rates south of the border.
The manifesto sets out a timetable for the implementation of Conservative plans for English votes for English laws within a year of the May 7 General Election and a promise to extend it to financial issues, in reflection of the devolution of tax-raising powers to Scotland.
The Smith Commission, which enshrined the vow of more powers for Scotland made before the referendum, states: "MPs representing constituencies across the whole of the UK will continue to decide the UK's Budget, including income tax."
Speaking on a visit to a children's workshop in Glasgow, Sturgeon said Cameron's announcement was a "direct breach" of the Smith Commission proposals.
She said: "But I've made clear on a number of occasions that if there are matters that are genuinely English only, that have no impact in Scotland, I think there's a strong case for Scottish MPs not voting on them.
"The problem is there's a lot of issues characterised as English-only issues that are anything but - matters relating to the English health service for example. Decisions taken on that have a direct impact on Scotland's budget."
Sturgeon said she would vote against anything that "prevented Scottish MPs standing up for Scotland's interests".
Chancellor George Osborne marked the publication of the English manifesto by posing for photos with a flag of St George in a pub in shadow chancellor Ed Balls's Morley and Outwood constituency. Osborne said he was "proud" to fly the red and white flag, which he said had been "recaptured" over recent years.
Former prime minister Gordon Brown last night accused the Tories of "whipping up anti-Scottish feeling" and becoming "the party of English nationalism".
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Sturgeon said Scots would be listening to what Cameron is saying and contrasting it with what he said during the referendum campaign.
She said: "Back then, it was 'Scotland's got a right to make its voice heard in the UK, Scotland should seek to lead the UK, not leave the UK', now it's, well, that only counts if we do what he wants us to do and vote how he wants us to vote.
"If Scotland chooses to make its voice heard by voting SNP, because it knows Scotland will stand up for Scotland and make our voice louder, then that's perfectly legitimate and David Cameron, frankly, should stop suggesting otherwise."
Sturgeon also outlined how she plans to divide a minority Labour government by convincing its backbenchers to back her policies at Westminster.
"If we are in a minority Labour government situation, with a big team of SNP MPs, what we will be doing is trying to build alliances on an issue-by-issue basis," she told The Herald.
"That will be trying to win support from Labour backbenchers as well as from Greens, if there are Greens, and from Plaid Cymru MPs."
Sturgeon again reiterated that she wasn't "planning" another referendum, and said she would not be pressured into proposing one in the 2016 Holyrood manifesto by members.
She said: "They are a very pragmatic bunch, who understand the realities of politics. "They also understand this democratic point: that Scotland will only be independent when a majority of people want Scotland to be independent.
"No matter how much we might want to rush that process, the Scottish people will not allow it to be rushed."
Last night, Sturgeon said the SNP could prop up a minority Labour administration even if Ed Miliband's party ends up with 40 fewer MPs than the Conservatives.
Sturgeon also spoke of how she will decide whether or not to include a referendum pledge in her next manifesto, saying she would "know in my gut", and that it would depend solely on what the people of Scotland wanted, rather than her SNP party.
Liberal Democrat leader Willie Rennie said: "Nicola Sturgeon's gut should remember that Nicola Sturgeon's mouth said there would not be another referendum for a lifetime."
Scottish Conservative leader Ruth Davidson said English-only income tax "completely fits in" with the Smith Commission.