A CONSTITUTIONAL expert, who has suggested a multi-question referendum on Scottish independence is feasible, has been appointed as an adviser to First Minister Alex Salmond.

However, Professor Stephen Tierney has also said the "real controversy" of a multi-question poll will come in making a decision on what the results mean.

The UK Government is opposed to a two-question referendum on independence and devo-max, believing it will lead to confusion and even a legal challenge.

The Scottish Government, while expressing a preference for a single question on independence, has said it is open-minded on a second one and is expected to make a decision in the autumn when the responses to its consultation are made public.

Increasingly, Whitehall figures and political opponents of Mr Salmond believe he is edging towards supporting a second question because, they argue, he fears he will lose if there is just a single one.

Prof Tierney, who is Professor of Constitutional Theory and director of the Edinburgh Centre for Constitutional Law at Edinburgh University, is being taken on to "give technical advice" on issues including the design of the ballot paper and structure of the poll, including the question or questions.

Already, Mr Salmond has agreed to the Electoral Commission, the UK's elections watchdog, advising on the proposed question – or questions – with Holyrood having the final say.

In February, giving evidence to the Commons Scottish Affairs Committee, Prof Tierney told MPs most referendums had just two options.

"Having said that," he explained, "under the international guidelines... there are clearly no rules against it [the multi-option poll]. If we were to take the deliverance of democracy point of view, one might say that there might be an argument to be put for giving voters more choice rather than less."

He added: "The real controversy possibly turns on how you make the decision when you have more than two options."

Last night, the Mr Salmond said he was delighted Prof Tierney had agreed to become an independent expert adviser to the Scottish Government, while the academic said he was honoured to accept the role.

He added: "I will provide independent, objective and publicly-available advice."

The SNP's political opponents decried the fact that Mr Salmond had turned down their offer of the creation of a panel of experts advising on the referendum.

Jackson Carlaw, the Scottish Conservative deputy leader, said it was sad the FM seemed "determined to do his own thing to suit his own narrow interests".