Alex Salmond is prepared to compromise on the Scottish independence referendum by including an extra question on giving Holyrood much greater financial freedom while remaining part of the UK.

The Scottish first minister said on Sunday he would talk to other parties about offering the voters a second choice known as "fiscal autonomy" within the UK, rather than a straight yes or no vote on Scotland moving to complete independence.

Speaking on the BBC's Politics Show, Salmond indicated he would work with opposition parties and other interest groups on the alternative question. "I'm very open to discussion and dialogue. Just because we got a majority in the Scottish parliament doesn't mean we've got a monopoly of wisdom," he said. "I will listen to what people have to say. I don't just listen to the SNP."

His offer came as a deep split emerged in the Tory party after senior Conservatives, including the Scotland Office minister David Mundell, said Salmond should be forced into staging a snap referendum rather than dragging out the debate for another four years. Mundell was joined by Murdo Fraser, deputy leader of the Scottish party, and Lord Forsyth, who was Scottish secretary in the previous Conservative government, in questioning a promise by David Cameron this weekend that the UK government would not interfere in Salmond's referendum plans.

Mundell, the only Tory MP in Scotland, said Westminster could get involved if an early referendum was rejected by the Scottish parliament. "Westminster obviously has a direct interest in this matter and could always get involved. I think it is perfectly legitimate for a referendum to be brought on," he said.

But Michael Moore, the Scottish secretary in the UK cabinet and Mundell's boss at the Scotland Office, immediately ruled out any prospect of the coalition government calling a snap referendum. Cameron told Salmond on Friday night that Westminster would not interfere with the Scottish parliament or raise legal or constitutional barriers to the plebiscite. Moore said: "As a UK government we will not be putting obstacles in the way of any referendum."

Forsyth, one of the fiercest Tory critics of devolution, said he had told Cameron about his strong reservations and would put down an amendment to the Scotland bill going through Westminster for a vote in the autumn. "I have been arguing for years that we should pick up Alex Salmond's challenge and get an independence referendum out of the way for a generation, rather than let Alex Salmond determine the vote," he told the Mail on Sunday. Officials in the last Labour government insisted a referendum would breach the Scotland Act 1998, which established the devolved parliament, since the constitution is reserved to Westminster.

Salmond is adamant that as the referendum will be consultative, and not legally binding, it is lawful. He has been given complete command of the referendum process after the SNP's unprecedented landslide victory in last week's Holyrood elections, winning 69 seats and an overall majority of the 129-seat parliament. For the first time, a Scottish government does not have to form a coalition or run a weak minority government, as the SNP did in its first term in power after securing a one-seat advantage over Labour in 2007.

Despite the clamour from his Tory opponents, Salmond again dismissed any prospect of the Scottish government holding the referendum immediately, saying he would wait until the latter stages of the five-year term.

He said this was a "democratic point", adding: "That's the plan we outlined to the Scottish people very clearly in the election campaign. We did so consistently and we have been backed overwhelmingly by the Scottish people on that prospectus."

The re-emergence of the so-called "devolution max" option – staying in the UK but with significant autonomy for Scotland – confirms that Salmond wants to give the referendum as much political legitimacy as he can, allowing him to kill off a unified, cross-party opposition campaign.

His proposal could attract opposition parties such as the Liberal Democrats, who favour federalism and are now desperate to regain political credibility in Scotland. That would dilute the anti-independence campaign both Cameron and Moore have said they will join.

It also allows the SNP to offer sceptical voters a potentially more attractive middle way in case his attempts to build up greater popular support for independence over the next four years fail to secure a majority. Despite Salmond's victory last week, opinion polls have repeatedly shown that less than a third of Scots favour full independence. Social attitudes surveys show instead that most Scots want to remain in the UK, but with much greater powers for Holyrood.

Ed Miliband, speaking on BBC1's Andrew Marr Show, said he believed Salmond would lose an independence referendum. But he conceded that Labour had suffered a "very, very bad result" in Scotland because it had failed to set out a "compelling and clear alternative" to the SNP's plans.

"I think what he is proposing is dangerous in terms of separatism," Miliband said. "I actually don't think that the majority of people in Scotland want independence or separatism. Now we've got to argue strongly against it if there is a referendum. I'm convinced we can win that argument."

Poll of polls

The AV referendum proved a disaster for electoral reformers – but a triumph for the Guardian's pollsters, ICM. The Guardian's final poll of the campaign, published online as the country prepared to vote, was spot on to one decimal point – making it possibly the most accurate poll ever. The published figures, after rounding the percentages, put the no camp on 68% against yes on 32%. ICM's actual prediction was no 67.9%, yes 32.1%. The Electoral Commission's final calculation was identical. Chance must have helped — but in this case the result was in before the first ballot paper had been counted.