Cameron and Miliband turn on Salmond

He said he was "100%" in agreement on the issue with Labour leader Ed Miliband, who told MPs that Scotland and the rest of the UK were "stronger together and weaker apart".

Mr Miliband called on supporters of the Union to make a positive case for its continuation, warning the Commons: "This is a momentous decision which our children and grandchildren will have to live with if we get it wrong."

The display of unity at Prime Minister's Questions came a day after Scottish First Minister Alex Salmond announced a preferred date of autumn 2014 for the independence referendum.

The First Minister told Westminster politicians to "butt out" of the debate over the timing and format of the referendum, following the UK Government's publication yesterday of a paper which argued that the Holyrood Parliament has no power to call a poll.

The consultation paper proposed that the Westminster Parliament could make an order to devolve power to Holyrood to stage a ballot on the single question of independence, which could take place within the next 18 months.

But Scottish National Party MP Angus Robertson today accused Mr Cameron of following in the footsteps of Margaret Thatcher by seeking to dictate to Scotland.

"The Scottish Government was elected with an overwhelming mandate to deliver an independence referendum in the second half of the parliamentary term," Mr Robertson told MPs.

"In contrast the Conservative Party has less Members of Parliament (in Scotland) than there are giant pandas in Edinburgh Zoo.

"So why is the Prime Minister trying to emulate Margaret Thatcher by dictating to Scotland?"

Mr Cameron said it was "quite the opposite" as the Government was offering Scotland the power to hold a legal referendum.

He added: "Right across this House there is uniform belief that that needs to happen."

Mr Cameron taunted the SNP for wanting to delay holding the independence vote, telling MPs: "I sometimes think when I listen to them that it is not a referendum they want, it's a never-endum."

The Prime Minister said: "Let's have the debate and let's keep our country together."

He added: "I passionately believe in the future of our United Kingdom. I passionately believe we are stronger together rather than breaking apart.

"Frankly, I am sad we are even having this debate, because I support the United Kingdom so strongly, but we have to respect the fact that Scotland voted for a separatist party at the Scottish parliamentary elections.

"The first thing that is right to do is to make clear the legal position about a referendum, and that is what the Scotland Secretary (Michael Moore) has been doing.

"We have made the offer that we will devolve the power to hold that referendum, so a referendum can be made in Scotland and held in Scotland.

"Frankly, I look forward to having the debate because I think there have been too many in the SNP who are happy to talk about the process, but they don't want to talk about the substance."

Mr Cameron said he wanted the UK Government and Westminster Parliament to talk directly with the Scottish Government and Holyrood to reach a swift conclusion on the timing and format of a referendum, which he insisted must be "clear, decisive and legal".

Mr Miliband called for immediate cross-party talks to deal with the process of how a single-question referendum can be held under the oversight of the Electoral Commission.

But he said it was vital that pro-Union politicians move quickly on to debating the substance of the issues surrounding independence for Scotland.

"We on this side of the House believe the United Kingdom benefits the people of Scotland and the people of the rest of the United Kingdom in equal measure," said the Labour leader.

"We are stronger together and weaker apart.

"We must make the case for the Union - not simply against separatism, but the positive case about the shared benefits to us all of Scotland's part in the United Kingdom, the shared economic interests, the shared institutions like the NHS, our defence forces and the BBC and above all the shared values we hold together."

Mr Miliband added: "We need a serious, thoughtful and inclusive debate on what the choices are and the benefits to Scotland of staying in the UK. On this one issue, the people of our country deserve nothing less than that serious debate about the benefits of the United Kingdom."

Mr Cameron's spokesman indicated that the Prime Minister himself would be involved in talks over the coming weeks, and is "sure" to speak directly with Mr Salmond at some point, though no meetings have yet been set up.

Mr Salmond today rejected the UK Government's argument that the Scotland Act of 1998, which established the devolution settlement, did not grant Holyrood the legal power to stage a referendum.

Announcing the Government's plans yesterday, Mr Moore said that the Act made clear that any referendum Bill passed in the Scottish Parliament would be open to a successful legal challenge in the Supreme Court.

"To legislate for a referendum on independence, the Scottish Parliament must have the legal power to do so," said Mr Moore. "It is the Government's clear view that the Scottish Parliament doesn't have that legal power."

The Government was ready to grant Holyrood that power by passing a "section 30 order" or to use legislation in Westminster to pave the way for a referendum, he said.

But when asked today if his plans were legal, Mr Salmond said: "Yes, we believe so."

There was "plenty of legal authority" to support Scottish Government proposals to mount its own ballot, he said.

The SNP leader accused Westminster of trying to interfere in Scottish affairs, and said the Prime Minister should "butt out".

He told BBC Radio Scotland's Good Morning Scotland programme he had "no objection" to a section 30 order, but added: "The objection, of course, is that the Prime Minister has started to put all sorts of London-based strings on.

"The Prime Minister came in with his size 10 boots and started to put all sorts of strings and conditions, and basically wanted to pull the strings of Scotland's referendum."

Mr Salmond said there had been a "huge adverse reaction" north of the border to "the Thatcheresque idea that Downing Street knows best".

The First Minister continued: "Our conditions are quite clear: this must be a referendum built and run in Scotland, accountable to the Scottish Parliament. It has to be run fairly and transparently, of course, but we won't accept unreasonable conditions placed by London on how Scotland should run the poll."

The order proposed by Westminster would require any referendum to take place under the oversight of the Electoral Commission, with a single ballot paper offering voters the choice between independence or remaining part of the UK.

Those registered to vote in Scottish parliamentary elections would be entitled to take part.

But the SNP has previously suggested an independence referendum could be opened up to those aged 16 and 17, with Mr Salmond saying today: "If you're having a vote on Scotland's future, 16 and 17-year-olds on the electoral roll have a stake in the future of the country."

While the Scottish Government has clarified when it plans to hold an independence referendum, ministers have not set out what question - or questions - will be put to voters.

Mr Salmond's spokesman said last night the "preference" was for a yes or no question on independence, but added they were "entirely open" to people also being given the option to vote for greatly enhanced powers for Holyrood.

Former chancellor Alistair Darling said Mr Salmond had "put off" holding a referendum until 2014 because he "doesn't think he can win just now and he is playing for time".

The Labour MP for Edinburgh South West told BBC Radio 4's Today programme that much of Scotland's political history over the last 40 years had been dominated by "process and political squabbling".

But he said: "Get the process sorted out, let us get on to the merits of the argument, because the sooner we treat people in Scotland like the grown-ups we are and we have a proper discussion about that, the better it will be."