ALEX Salmond has defended the right to claim a simple majority in a referendum as a mandate for independence, even if more voters opted for "devolution max" in a multi-choice poll.

The First Minister argued all of this was spelled out in the referendum Bill white paper in February 2010 and followed the precedent of the 1997 referendum, which had one vote for a Scottish Parliament and a second to give it tax-varying powers.

However, Professor John Curtice of Strathclyde University dismissed the comparison with 1997, saying next time there could be two very different “Yes” outcomes: One for extending devolution and the other for independence, which would require new rules for determining the outcome.

He insisted that in 1997 the two questions were more clearly linked, with one vote establishing a parliament and a second giving that parliament a specific power. “Devo max and independence can be seen as two separate questions and we cannot assume that everyone voting for independence would prefer that to devo max,” he said.

“If people see these are two separate questions and are then told that the one that is implemented is the one that got less support, they will say no way.”

The SNP said if there was a first question on extending devolution and a second for independence it would give options to vote No-No for the status quo, Yes-No for devo max, or Yes-Yes for independence – with No-Yes as impractical an option as it was in 1997.

But Yes-Yes would almost inevitably receive fewer votes than Yes-No as opposition to independence kicked in.

Mr Curtice said the answer was an alternative vote poll, but when the SNP mooted that in 2010 the other parties shot down the idea.

Scottish LibDem leader Willie Rennie insisted: “It is time the SNP abandoned the smoke and mirrors and explained how they can possibly justify how a tiny majority for independence could trump a landslide for devo max.”

A spokesman for the First Minister said: “The SNP Government has always made it clear that we are entirely willing to include a ‘devo max’ option in the referendum.”