A CONSTITUTIONAL crisis is looming between Westminster and Holyrood as Coalition sources become increasingly convinced that Alex Salmond will seek a second question on the referendum ballot paper.

Senior Whitehall sources believe the First Minister will use the publication of the consultation exercise on the referendum to push for a second question on so-called devo-max.

While only 12% of respondents to the UK Government's consultation supported a second question on more powers for Holyrood, it is expected this figure will be much higher when the results of the Scottish Government's consultation are published in the autumn.

One senior Coalition source asked: "Why would Salmond hold a single question when all the polls show he is going to lose it? A second question would be his parachute."

Another said: "Salmond is now running scared. The idea he wants a second question is gaining currency here."

At the weekend, Alistair Darling of the No campaign said: "It's obvious to me, to put it bluntly, he wants two questions because he is frightened of one."

The First Minister and other key SNP figures have made clear their preference for a single question but acknowledge there is a support for a second one.

On Sunday, Stewart Hosie, the Nationalists' Treasury spokesman at Westminster, said: "The case for independence trumps any case for further devolution but there are those who believe in further devolution and, of course, they should be allowed to test that against independence and the status quo."

A Holyrood source said Mr Salmond and his colleagues were "open-minded", stressing: "The potential options on offer should not be foreclosed, certainly not by the UK Government."

A Scottish Government spokesman made clear its policy was for independence, but recognised there was "substantial support across Scotland, from individuals and organisations, for increased responsibilities for the Scottish Parliament short of independence".

Among those supportive of a second question are the Scottish Trades Union Congress and the Scottish Council for Voluntary Organisations.

More than a month ago, Michael Moore, the Scottish Secretary, invited Mr Salmond to hold urgent talks on technical aspects, most notably a Section 30 Order, which would ensure Holyrood could hold a legal poll.

The First Minister replied, but said there had been 21,000 responses to the consultation and these had to be analysed; the implication being no talks would take place until publication of the responses.

David Mundell, the Scotland Office Minister, and Bruce Crawford, the Scottish Government's Parliamentary Business Secretary, are due to meet in late July or early August.

While Westminster has offered a Section 30 order, its offer is predicated on there being a single question. If Mr Salmond pressed ahead with two questions without a Section 30 Order, the Coalition believes it will be challenged in a court of law.

Agreement on a parliamentary order has to be agreed not only by both Houses of Parliament and the Scottish Parliament but also by the Privy Council, which only meets every three months.

If the talks become deadlocked for any length of time, then the autumn 2014 timetable could be put in doubt.