SEVEN months after the SNP's landslide victory in the Scottish election, the Unionist parties still lack a concerted strategy to address its biggest consequence: the inevitability of a referendum on independence.

Alex Salmond's continuing commitment to hold the referendum in the second half of the parliamentary term, however, has had the effect of uniting the Unionist parties in calling for it to be held earlier.

Because Westminster retains power over the constitution, a referendum held by the Scottish Government would technically be consultative rather than legally binding, although an outright majority in favour of independence would have an unassailable political and moral force. An amendment to the Scotland Bill to give Holyrood the power to hold a legally-binding referendum, would overcome the possibility of a legal challenge that would significantly delay the whole process. This would have the benefits of clarifying the situation and reinforcing the enormous significance of the vote. However, it appears that thinking in Whitehall, and among some members of the House of Lords, is that there should be a quid pro quo requiring the referendum to be held much sooner than planned by the SNP.

The chief argument for accelerating the timetable put forward by the Coalition, and yesterday by former Tory Scottish Secretary Lord Forsyth, is that it will end uncertainty which is said to be hindering business investment in Scotland.

The political dimensions cannot be dismissed, however. While all three Unionist parties have been distracted in adjusting to the new political landscapes on both sides of the Border, the SNP has been able to claim a mandate for holding the referendum post-2014, making demands for a quicker resolution in danger of looking like sour grapes. Their high profile as the party of Government in Scotland and £2 million war chest mean the Unionists will face a considerable challenge in matching their campaign. That will require a cross-party strategy but that is likely to be problematic because, as we reveal today, Cabinet ministers are insisting that the anti-independence campaign must be led by David Cameron.

The Prime Minister of the United Kingdom will inevitably play a key role in supporting the UK as an entity and it would be unthinkable for Mr Cameron, who has vowed to defend the Union with every fibre of his being, to be anything less than highly visible in favour of the status quo. The conviction of the Cabinet that he should lead the charge, however, reveals that ministers are either dangerously detached from opinion in Scotland or cavalier about the consequences.

A referendum is a vote on an issue and not for a candidate, so personalities should matter less than in an election. Nevertheless, a campaign led by an English Tory born into wealth and privilege could only play into the Nationalists' favour, given that the Conswervatives remain a toxic brand in parts of Scotland.

To win a referendum vote, the Unionist parties need to run a joint campaign with politicians who have established credibility in Scotland from all three parties.

This is proving a problem. Jim Murphy, the former Scotland Secretary, for example, has already refused to share a platform with David Cameron. Those now in the House of Lords, such as John Reid,who has already stood shoulder-to-shoulder with Mr Cameron in opposition to change to the voting system for General Elections, may decline to pick up the gauntlet. It is essential, however, that the people of Scotland are presented with clear and reasoned arguments about the far-reaching consequences of their vote. The reality of the future of the economy, the armed forces, membership of the EU and foreign relations are of greater significance than the date of the referendum.