JOHN SWINNEY has written to the Prime Minister to demand talks to agree a legal mechanism to trigger a second referendum on independence.

The First Minister took the step after Andy Burnham suggested during Wednesday’s Prime Minister’s Questions that a rerun of the 2014 plebiscite could be possible if public opinion shows demand for one, an apparent shift from his earlier instance it was “off the table.”

The Prime Minister told MPs that Scotland should be in “exactly the same situation” as Northern Ireland, where the Good Friday Agreement provides for a border poll should the Northern Ireland Secretary believe there is “a clear consensus in the country, when public opinion has changed to the point where the call has to be considered.”

Stating he was not aware of any such consensus, he insisted: “Until that changes there won’t be one.”

Calling for a meeting with the Prime Minister to discuss “how we turn that principle into an agreed legal mechanism,” Mr Swinney argued: “By concluding a clear, understandable mechanism, both sides of the constitutional debate can move forward constructively.”

Speaking on BBC Radio Scotland, psephologist Professor John Curtice acknowledged polls presently “suggest there is at least a small majority in favour of independence.”

But he cautioned: “The real challenge the nationalists face is to get the numbers, which have been around 50/50 now for about seven years, up to something like the 60 per cent mark, where it will begin to look indeed as if some kind of vote is going to be difficult to avoid.

“We are not yet in that position, but equally we are not in as firm a position as unionists would like.”