At Prime Ministers Questions yesterday SNP MPs fell over each other to condemn the "constitutional outrage" of English Votes for English Laws (Evel).

They should welcome it with open arms.

I can't think of anything more likely to precipitate the final break-up of the UK than this crackpot scheme to exclude Scottish MPs (of all parties) from certain votes in the Commons. As I argue in my new book out today Tsunami; Scotland's democratic revolution (Cargo), Evel is the federalism of fools.

In fact, I'm beginning to wonder if the UK political establishment has realised, perhaps unconsciously, that the Union is effectively over. We have just witnessed the most remarkable electoral event in Scottish history: the May 2015 General Election in which the Unionist parties were all but obliterated.

Even the most blinkered Conservative MP must surely realise that Evel will weaken what remains of the sinews of union. It will marginalise Scottish MPs and further undermine Scottish voters' identification with Westminster.

The idea is to answer the West Lothian Question - Scottish MPs having a say in English affairs while English MPs have no say in Holyrood - by allowing English MPs to vote exclusively on bills that only affect England.

As David Cameron put it yesterday: "Laws which only apply in England should only pass if they're supported by a majority of English MPs."

But if Mr Cameron is serious, this would amount to the creation of a de facto English parliament. Indeed, it would potentially turn Westminster into an English parliament with Scottish MPs only having full voting rights on "federal" issues such as defence and foreign affairs.

The PM insists this is not what he intends to do. He doesn't want an English parliament; he doesn't want to create two categories of MP. But it is very hard to reconcile these protestations with the prospectus he outlined yesterday.

We haven't seen the Government's Evel plan in its entirety yet, but it's understood that it will call for English MPs to sit in a special English Grand Committee to vote on and amend English bills. The results would still go to the full House of Commons for a final vote. There would therefore be a legislative backstop.

But if, as the PM made clear at Question Time, no nominally English bill can pass without the agreement of English MPs, this backstop is meaningless. At the very least it would leave legislative deadlock between the English Grand Committee and the Commons.

A total of 553 MPs out of 650 in the Commons sit for English constituencies. Once they have the right to vote on the committee stages of English legislation on health or education, or indeed English taxation, they are hardly likely to accept their wishes being overturned by a small minority of Scottish and Welsh MPs.

This is the reason why most constitutionalists even in England have argued against English only votes. The Union Parliament is supposed to be unitary and indivisible, with all MPs equal. Evel disaggregates the Commons along regional lines.

Perhaps it is time for a federal constitution for the UK. There is clearly an anomaly in Scottish MPs voting on English issues such as fox hunting that are devolved to Scotland. But this is hardly the way to go about it.

Restricting the voting rights of Scottish MPs is arguably the most radical change in UK parliamentary practice since the Act of Union. Yet the Government isn't even planning to put Evel before the two Houses of Parliament in a coherent piece of legislation. It is presenting it as a mere procedural change on a vote on Standing Orders before the summer recess.

This isn't reform. It is the constitutional equivalent of a drive-by shooting. It means that the House of Lords, where there are many experts on the constitution, will not be able to review this fundamental change.

Some optimists believe that Evel could still spark a full scale federal restructuring of the United Kingdom, compete with the House of Lords turned into a regionally-elected Senate, a written constitution and English devolution. But this is naive.

This Government has no intention of turning the Lords into a senate, or legislating for English devolution and there are no plans for a written constitution. Evel has all the hallmarks of electoral expediency: a sneaky way to make it almost impossible for Labour to govern again across 85 per cent of the UK.

If English MPs are given a right to veto measures applying to England it would mean that any government with a Commons majority based on the votes of Scottish or Welsh MPs would not be able to implement its manifesto promises on health, education, criminal justice or the environment.

This is not just a Scottish issue. Evel could make cabinet government in the UK virtually impossible.

Imagine if Labour had won the General Election. It tries to repeal the 2011 Health and Social Care Act which allowed private providers to invade the English NHS. Under Evel it would not be able to do this because a majority of English MPs on the English Grand Committee would be Conservative and would veto it.

Mr Cameron says the principle of Evel has already been accepted by the Nationalists. The SNP has tacitly recognised the unfairness by voluntarily withdrawing from votes on exclusively English bills (though they have been under intense pressure from anti-hunt groups to renege on this promise and vote against restoring fox hunting in England).

However, the problem is that very few bills are exclusively English. Legislative responsibility for health and education are devolved, but they are still financed collectively on a UK basis. Changes such as the privatisation of the English NHS affect the funding of the service in Scotland through the Barnett Formula.

This brings us to the Scotland Bill, all amendments to which have been rejected by the UK Government even though it has only one MP in Scotland. Clearly, Scottish votes for Scottish laws is not on the reform agenda.

SNP MPs tabled an amendment calling for full fiscal autonomy - despite having allegedly abandoned it - and it was rejected. Attempts to increase Holyrood's powers over welfare have been similarly rebuffed.

So it seems that the sum total of the UK Government's response to the SNP's electoral tsunami is to press ahead with Evel. The message that will be taken by Scottish MPs - and by many of the Scottish voters who supported them - is that Scotland can vote SNP as much as it likes, there will be no further concessions.

The UK Government presumably hopes that disappointed voters will lose faith in the SNP, especially when Holyrood tries to put up income tax to mitigate the effect of benefit cuts. They will realise there is no point continuing to support the "feeble 56". Indeed, voting SNP will be seen to make Scotland more marginal in the affairs of the UK.

This is a dangerous game, however. The message of 2014/15 is that Scotland has fundamentally reassessed its place in the Union. If Scottish voters believe that their MPs no longer have equal voting rights in the UK Government, they might well conclude that there is little point in having them there in the first place.