From an English perspective David Cameron's most recent speech on the Union is marginally better than his previous big speech on the Union - also delivered to a Scottish audience - in which he blamed the rise of Scottish separatism on English ignorance and promised to fight 'sour Little Englanders' all the way. David Cameron probably decided to leave the English out of Thursday's speech after reading that the Institute of Public Policy Research found that only one in four of the English support the status quo; that 59% of the English do not trust the UK government to work in the best long-term interests of England, with 79 per cent saying that Scottish MPs should be barred from voting on English laws, and; that 80% of English people support Devo-Max for Scotland. It was a calculated mistake; England, and the wants of the rest of the United Kingdom, complicate the argument for Unionists in a way that does not trouble the SNP.

David Cameron (or rather Westminster) may have the legal right to prevent a binding referendum on Devo-Max but he does not have the moral right. Cameron, however, has gambled big by stating that the case for Devo-Max, the preferred choice of both the Scots and the English, cannot be an considered until after the Scots have rejected independence. This is snake oil salesman territory. Cameron will not consider Devo-Max as it is understood by the Scottish public because, as one questioner put it, "devo max is something that possibly poses as much a threat to the present state [status quo] of the United Kingdom as independence." Or to use Lord Forsyth's turn of phrase: "Devo max would mean creating an English Parliament and a federal government".   Fiscal federalism of the kind that 'Devo-Max' entails would arguably have more profound consequences for the Westminster bubble than the loss of Scotland.

Even if federalism were a desirable outcome from a Conservative perspective, Devo-Max would still not be an option because it requires the consent of four nations - not just the Scottish people - and there is no Unionist blueprint for such an eventuality, nor any roadmap that could be rolled out in time for Autumn 2014. So Cameron is left flogging a product that he and his Scottish audience do not understand. Will the quasi-federal Union that Cameron wants the Scottish nation to buy into be one in which Scottish MPs are prevented from voting on 70% of Westminster legislation, logically, therefore, excluding Scottish MPs from ministerial positions with an English portfolio? Will it be a Union in which reform of the Barnett Formula will trim Scotland's budget by £4.5 billion? Will it be a Union in which Scotland has proper tax and spend powers or control over oil revenue? Or will it be a Union in which Scotland has greater non-fiscal powers but in which Scottish Government policy is shackled - via Barnett - to those of the UK Government's in England, while the unwanted status quo remains a reality for a constitutionally discontent and increasingly nationalistic England?

Unionists need to answer these questions prior to the referendum on Scottish Independence.

We need to know exactly what manner of Union Cameron is asking the Scots to vote for? In refusing to countenance Devo-Max, and by ignoring the English, Cameron belies his claim that "The Union has never been about shackling different nations: it is a free partnership".

In what way is it a free partnership if the Scottish are not permitted a vote on Devo-Max and the English are never even consulted?