Cameron has conceded that Westminster can have no say in the conduct of the Scottish referendum on withdrawal from the Treaty of Union. Not allowed, not graciously gifted or what ever other gloss Westminster and its media minions try to put on it - conceded; lock stock and barrel.
The legal and constitutional reality is that Westminster has never had an legal or quasi legal role to play in the referendum as the Treaty of Union makes clear: any alteration of the Treaty of Union can only be carried out by the sovereign parliaments of Scotland and England and not Westminster. Further Cameron is conceding the referendum reflects the considered will of the people of Scotland (UK Supreme Court - AXA et al), in doing so Cameron is tacitally admitting a coach and horses has just been driven through sections 5 & 30 of the 1998 Scotland Act as well as Westminster's illegitimate claim to 'unlimited sovereignty' over Scotland. (Lord Cooper: McCormack 1953).
Westminster having dug a dirty great big hole for itself over both these unsustainable claims and has now fallen to the bottom. The question remains - will they keep digging or try and find a way to scrabble out?
Let us consider Westminster's next potential volte face; full fiscal autonomy - many Scots declared preference. After the likes of Ian Davidson and other Scottish New Labour MPs have swallowed large slices of humble pie and through gritted teeth found some faux enthusiasm for a project they deeply hate; could it happen?
The fly in the ointment then becomes the English electorate whom Westminster have spent the last eight years feeding the negative 'England subsidises Scotland' spin. Remember, I stated above the Treaty of Union can only be altered by the sovereign parliaments of England and Scotland and not Westminster. The problem for Westminster is while it could propose Full Fiscal Autonomy and pass a bill on the same, this bill will fundamentally alter the original basis of the 1707 Treaty of Union which it has no powers to do. Catch 22 in most respects. Westminster could only get around this by holding a binding referendum of the English electorate to agree Westminster, on their behalf as the sovereign English Parliament, can undertake alteration of the 1707 Treaty of Union to a new Confederal Union which is what FFA creates.
For Scotland agreement of a new Confederal Union could be passed by a simple majority in the Scottish Parliament as long as the Scottish Parliament Act reflected the considered will of the Scottish people by doing so.
Here is the problem. After all these years of Westminster banging on about how much the English subsidise the Scots what English elector would wish this to keep on going in any form. UKIP will have a field day or be left looking very stupid. How can UKIP oppose the EU while supporting an equally, in English eyes, lopside settlement within the new Union? There is a general sense, ignoring the rabid unionist posters, the English Electorate does not see the same levels of toxicity and harm in the concept of Scotland and England returning to being independent nations sharing the same island - letting Scotland go and good luck appears to be the norm.
To win a FFA referendum to give Westminster authority to act as the 'English Parliament' has two major groups to win round; let me call them the Union extremists (Federal UK -over our dead bodies) and the fundamental apatheticists (Oh, just let the Jocks go and good luck to them). I would suggest these two groups reflect the majority view in England, as far as it can be discerned.
This leaves the Scottish wings of the Westminster parties with only two options: to support the 'No' campaign or agree that withdrawal from the Treaty of Union and a return to Scottish independence is inevitable. In realistic terms Westminster bringing forward an FFA bill is a non-starter as by doing so they create a clear win / win situation for the 'Yes' camp. Even if the Scots vote for FFA the current best guess is the English Electorate will oppose FFA as there is nothing in it for them they could not gain by independence.