Scotland braced for cross-border raids from Westminster Westminster heavyweights are lining up visits to Scotland in the next few weeks as the campaign to save the Union picks up steam. David Cameron and a host of other current and former ministers will lead the charge against Scottish independence, attempting to move beyond the complex debate about the terms of a referendum, which they believe only benefits Alex Salmond and his fellow Scottish nationalists. The prime minister told MPs on Wednesday: "I am looking forward to having this debate. There have been too many in the SNP who are happy to talk about the process of a referendum but don't want to talk about the issue of independence. He accused Mr Salmond of wanting a "neverendum, not a referendum." He was immediately challenged by Angus Robertson, the SNP leader in Westminster, who said Mr Cameron was "trying to emulate Margaret Thatcher by dictating to Scotland." Coalition ministers are concerned that the spat over the timing of the referendum and the options it should offer voters has proved a distraction and allowed Mr Salmond to accuse Westminster of interfering in Scottish issues. They are keen to begin an informal campaign to keep Scotland in the United Kingdom even before details of the referendum have been settled. Michael Moore, the Scotland secretary, has pressed cabinet colleagues in recent days to spend time in Scotland making the case for the Union. Caroline Spelman, the environment secretary, will begin that drive today when she meets Scottish farmers. Other prominent figures in the campaign will include Vince Cable, the business secretary and former Glasgow councillor, Chris Huhne, the energy secretary, Sir Menzies Campbell, the former Liberal Democrat leader, and Alistair Darling, the former chancellor. But behind the scenes, officials are still concerned about how to get Mr Salmond to agree to a legally binding referendum, the terms of which would have to be agreed in Westminster as well as Holyrood. They admit it will be difficult to avoid a constitutional confrontation, given the gulf that separates the SNP from the other parties on four issues: when the referendum will be held; who will be eligible to vote; how the voting process will be supervised; and whether the ballot paper will include a third option of enhanced economic powers - often known as "devolution max" - as well as a "Yes or No" vote on independence. Mr Cameron yesterday pressed Mr Salmond to hold the referendum earlier than the first minister's chosen date of autumn 2014, the 700th anniversary of the battle of Bannockburn, when Scotland will also host the Commonwealth Games and Ryder Cup. But the coalition has already backed down on insisting on an 18-month time limit, suggesting there is scope for compromise. Westminster officials, meanwhile, expect Mr Salmond to back down on his insistence that the franchise is extended to 16- and 17-year-olds and that the Electoral Commission is not the body used to oversee the process. The option of "devolution max," however, is likely to be the one issue on which attempts to reach a compromise founder. Although Mr Salmond has said he would prefer a simple "in/out" referendum, he has been at pains to leave the door open to this third alternative, which is currently more popular. The devo max option is toxic for the Unionist parties - not least because they would struggle to agree on what would be ceded. One UK official said: "It has taken two years to agree on the powers that are currently being handed over in the Scotland bill - how long would it take to figure out what devo max means?" Only one thing is certain: ahead lie months of hard bargaining and politicking between Holyrood and Westminster.