WHEN the Scottish people voted in unexpected numbers for the SNP last May, they were not endorsing its founding principle of independence for Scotland but they knowingly gave Alex Salmond a political mandate to hold a referendum on independence in the second half of the current parliamentary term.

Under the Scotland Act 1998 constitutional matters are reserved to Westminster. This raises both the question of the legal power of the Scottish Government to hold a referendum on whether Scotland remains part of the United Kingdom – and the political temperature. The UK Government has been advised that Holyrood does not have the authority to pass legislation to trigger a referendum and that raising such a Bill at Holyrood would result in a referral to the Supreme Court either by the law officers or by an individual. That would further increase tension in the Union and resentment in Scotland at perceived interference from London in the democratic will of Scots.

The Coalition solution is to transfer the power to hold a legally binding referendum. This would be both pragmatic and proper if the terms and detail were left to the Scottish Parliament since Scots voted in their Government at Holyrood and would mark their preference in the referendum. The Coalition has begun a three-month consultation period on the proposals. Scotland Secretary Michael Moore favours a single yes/no question with the ballot being held within 18 months.

Alex Salmond, not noted for being risk averse, last night appeared to call Westminster's bluff by announcing the SNP's own plans: a referendum in the autumn of 2014 and a separate consultation process launched later this month.

This war between the SNP and Westminster, lacking light but not short of heat, is in danger of diverting attention from the substantive issue. If the UK Government is prepared to give Holyrood the power to hold a legally binding referendum, there is a strong case for doing so with no strings attached to the transfer of authority. Both sides are wrangling over the date for possible political advantage. Now that Mr Salmond has announced his time frame, what would Mr Moore and his Coalition colleagues have to gain by insisting that it is shortened by possibly nine months or so?

Devolution is a process. If it were not so, we would not be in these extraordinary times. Scotland's future is up for grabs but should that future be decided on a straight yes/no question? Given that support for increased power for "devolution max" or independence lite, giving Scots that option to consider on a ballot paper deserves full and proper scrutiny.

The battle lines have become clearer. But a stand-off is in no-one's interest. Now is the time for both sides to engage in mature debate, starting with agreement on the transfer of authority to hold a referendum that is, in Mr Moore's words, legal, fair and decisive. When there are so many other challenges facing Britain and Scotland, meeting these criteria must not be all-consuming. Once met, it will be time for Scots to decide their destiny.