FIRST there was one option, now there is a whole raft of them.

No sooner had Alex Salmond and David Cameron struck the Edinburgh Agreement, and opened the way for a single-question referendum on independence for Scotland, when along come the Liberal Democrats with plans for a full-scale federal restructuring of Britain. The Scottish Labour Party has also finally convened its Devolution Commission. And of course David Cameron has suggested that Scotland can expect enhanced devolution if we are good boys and girls and reject independence. Suddenly you can't move for devolution commissions. What will Scots make of it all?

Well, the Liberal Democrats first. Their Home Rule Commission under the former leader, Sir Menzies Campbell which reported this week, has essentially restated their long-standing policy of federalism. The LibDems want a formal separation of powers between a federal UK level of government and subordinate state governments in the component parts of the UK. Much like the United States of America – though smaller. The Scottish Parliament would gain full powers over income tax and domestic policy, while leaving defence, foreign affairs and overall currency to a new level of government. It's a system that works very well in countries like Australia and Germany where federal systems were introduced by British colonial and wartime administrations.

But it would mean that English people would have to get used to voting for their own parliament, in a location yet to be identified, while also voting for a UK president or party at Westminster. And here lies the essential problem. English people are quite happy with their parliament in Westminster and don't see why they should go through some constitutional upheaval just because the Scots want a better deal. Northern English regions were given the opportunity to vote for regional parliaments in referendums on devolution in 2004 and the proposals were decisively rejected.

There is another problem: the Liberal Democrats. They have a massive credibility problem in Scotland, not least because of commitments made never to increase university tuition fees, which of course were abandoned when they came to office. Similarly, the Liberal Democrats promised electoral reform and reform of the House of Lords, neither of which ever saw the light of constitutional day. Which makes it hard to believe that their federal system will ever be adopted. Especially since they have just spent the last two years insisting that their proposal should not be put to the Scottish people in a referendum.

This really won't do. Sir Menzies says that the present constitutional settlement is "unsustainable" and that there needs to be a root and branch reform of the UK constitution. This is, to all intents and purposes, devolution max, yet they have insisted that there should be no opportunity for the Scots to give their view on it. The Liberal Democrats were happy to have a referendum on the Alternative Vote and say they want one on British membership of the European Union. About the only constitutional issue they don't want tested in a referendum is their own plan for a federal UK.

The Scottish opposition parties have expended so much political capital on blocking that second question that they've left themselves precious little for their own schemes. Labour has finally convened the Devolution Commission that was promised by Johann Lamont last March. Mind you, given the new Scottish Labour leader's predilection for abandoning cherished Labour policies like universal benefits, it's not inconceivable she might just decide to dump home rule as well. Who was Keir Hardie anyway? The Scottish Parliament begat the "something for nothing society" – free personal care, tuition fees and so on. So why not just get rid of the thing and save money?

The Tories probably aren't stupid enough to propose that, but they are so marginal now in Scottish politics that they can more or less say what they like. They know, as Ms Lamont knows, that if the Scots vote No to independence in the autumn of 2014 there will be no need to come up with complicated schemes of enhanced devolution. A No vote will be regarded as a vindication of the constitutional status quo, plain and simple. There will no longer be any need to honour vague promises of better things to come. The UK Government may agree to some kind of post-referendum review of the Scottish Parliament's powers, but this will report that the powers already conceded by the recent Scotland Act are pretty much the limits of constitutional autonomy within a unitary state.

No-one should be under any illusions that, if Scots vote No to independence, they will get anything remotely resembling devolution max or devolution plus, the latter being the proposal put forward by the Reform Scotland think tank who want all taxes repatriated except VAT and National Insurance. It just isn't going to happen. No so much new wine in old bottles as the bottles taken away in a skip. No means no.

It will be argued that, while subordinate levels of government can be given their own tax base, like local government, overall fiscal policy has to be set centrally by the central UK Treasury and backstopped by the Bank of England. Giving the Scottish Parliament further income tax-raising powers, or powers to create its own national debt, might lead to instability as it has in Spain, where the autonomous region of Catalonia has been running up deficits which Madrid doesn't want to pay. Can't have that.

So, the overwhelming majority of Scots, who want a new improved version of devolution but don't particularly want to leave the UK to get it, will soon discover that they have effectively been disenfranchised: allowed only to vote for options they don't actually support. The irony is that, if the Liberal Democrats' federal plan were put to the Scottish people in a referendum in 2014, the Scots would almost certainly vote for it. But of course it won't be, so they can't. The big question for the next 100 weeks is what the Scottish voters will do when they wake up to the fact that they have been locked out of their own referendum. I suspect many will not bother to vote, others will vote Yes out of frustration. Either way, it could undermine the legitimacy of the referendum.