Vernon Bogdanor: David Cameron should add second question to independence referendum Options for a second question include Mr Salmond's preference, devolution max or "devo max," whereby the Scottish Parliament would be responsible for setting and raising all taxes. "To suggest that there is a mystery prize which cannot be revealed until after independence is rejected is hardly satisfactory," Prof Bogdanor said in his written submission ahead of his appearance before the committee today. "A suspicious Scottish voter might fear that, if she were to reject independence, and if the SNP were then to be defeated in the Holyrood elections in 2015, Westminster might then forget about "devo max" and the status quo would be preserved." Prof Bogdanor, whose former students include the Prime Minister, said public support for extra powers means there is a "strong case" for the inclusion of a second question. This could be staged by inviting voters to tick one of three options - the status quo, extra powers or independence. If no option got more than 50 per cent, Prof Bogdanor said a second "run-off" referendum would then be staged between the two most popular options. But the academic, who is based at King's College in London, told the Daily Telegraph that voters cannot back both independence and more powers, as Mr Salmond wants. The First Minister has said that Scotland would separate if 51 per cent back independence, even if 99 per cent of people back more powers but staying in the UK. However, the professor said this was akin to giving the SNP a "let-out." He also rejected Mr Salmond's "very bad" question as asking voters whether they "agree" Scotland should be independent is biased. Instead his submission said the Electoral Commission should decide the wording. The SNP's delayed timetable "would be likely to harm the Scottish economy since businesses may be unwilling to invest in Scotland amid a climate of constitutional uncertainty," he said, citing Quebec's experience.