The Government has so much on its plate at the moment that it appears to have forgotten to make its case against the Brexit demands of the devolved administrations. Which is unfortunate, as this is a very important debate.

Nicola Sturgeon and Carwyn Jones, nationalists big-N and small, are demanding that a huge range of powers in ‘devolved areas’ currently exercised in Brussels be passed straight to Cardiff and Edinburgh.

That’s par for the course: demanding power is their invariable response to any constitutional question. But worryingly for the Government even staunch unionists are taking up their line. James Forsyth writes in the Spectator that ministers must “curb Whitehall’s instinct to hog all the powers”.

More seriously still, Adam Tomkins, a Tory MSP and law professor who represented the Party on the Smith Commission on devolution, has been pushing the Government to yield on this for a while, and has now broken cover in an op-ed for the Scotsman.

All are objecting to Section 11 of the Withdrawal Bill, which vests all returning powers in Westminster unless and until devolution agreements are reached at a later date. This is what nationalists are calling, Forsyth says “with some justification”, a ‘power grab’.

These arguments all share a common basis: that Holyrood and Cardiff Bay are morally entitled to these powers. Tomkins also argues, and Forsyth seems to assume, that most of these powers can be safely devolved without damaging the British internal market.

But Westminster has not made a habit of digging its heels in against the devolved administrations when retreat is an option. The Government – not, as Forsyth has it, ‘civil servants’ – adopted this tough-minded approach to Section 11, and they have a case even if they have neglected to make it.

In short, the basis of the Government’s position disputes the Tomkins/Forsyth thesis on pretty much every level: that this is a legal ‘power grab’; that the ‘spirit of devolution’ creates a moral obligation to pass the powers on; and that these powers will not disrupt the British internal market.

First, the law. Our sources argue that it is misleading to refer to these areas as straightforwardly reserved. Rather, powers currently exercised at the EU level are there by dint of pooled sovereignty between the member states. It is the British Government that puts powers into the European pot, not the Scottish, and it is British ministers who negotiate in Brussels on our behalf.

Thus, these powers are not descending from some higher plane (“neither Scottish nor British”, as Tomkins puts it) onto an unprepared British legal landscape, but are instead already Westminster powers, currently pooled in Brussels but soon to be withdrawn back to London.

Here is where the ‘spirit of devolution’ is usually summoned. But as near-everyone concedes, none of the architects of devolution ever imagined these powers being devolved. Westminster cannot be morally ‘grabbing’ powers from Edinburgh and Cardiff that the latter have never exercised nor ever were intended to exercise.

Moreover even if these powers weren’t already Westminster powers, the Scotland Act may provide that “all powers not expressly reserved to Westminster are devolved to Holyrood”, to quote Tomkins again, but doesn’t say that Westminster can’t reserve more powers to itself should the circumstances require it.

Both Tomkins and Forsyth concede that the claims of the devolved administrations flow from the sloppiness and lack of imagination with which devolution was drawn up, rather than any positive intention, but don’t recognise that this seriously undermines the moral force of those claims.

In fact, it potentially recasts the issue as a power grab against Westminster, based on an implausibly restrictive and self-serving reading of the reserved powers model by Sturgeon, Jones, and their allies. If the ‘spirit of devolution’ doesn’t represent the true intentions of those who drew devolution up, and it doesn’t here, then it is simply a wish-granting devolutionary genie which unilaterally reinterprets the constitution to Westminster’s disadvantage – for example, by recasting a need for the Government to consult with the devolved governments with a supposed need to get their consent.

This leads on to the practicalities. Section 11 was drawn up in the firm belief not only that the overwhelming majority of the 111 powers Tomkins discussed are essential to the smooth and effective operation of a single market, but that British institutions were the best vehicles for setting UK-level policy.

Our sources argue that things like food labelling and country-of-origin rules, whilst seeming boring and technical, can very easily snarl a common market if allowed to disharmonise. Even aircraft noise pollution, which Tomkins highlights as a clear case of a power Holyrood can safely have, is an important part of creating ‘open skies’ agreements.

If the Scottish Conservatives genuinely believe that the vast majority of the Single Market’s rules can be safely devolved (to the sub-state level, no less), they add, why did they back Remain at all? How have they ended up in the awkward position of echoing the nationalists, who maintain the anti-British position that powers acceptable when exercised by Brussels are intolerable if ‘imposed’ by London?

Under the current dynamics of devolution, powers passed down do not pass back. There is no precedent for re-reserving a power if devolving it produces bad outcomes. Section 11 is designed to park powers in Westminster until the impact of devolving them can be properly understood and, if appropriate, practical ways of doing so devised.

It would be grossly imprudent, albeit not unprecedented, for the Government to pass these powers down for the sake of a quiet life, and hope to claw together a workable arrangement later on in negotiations where the nationalists held all the cards.

Some fear that what the SNP really want, and what Carwyn Jones’ confederal proposals for managing the British internal market would give them, is an inexhaustible supply of opportunities to foul the smooth running of the Union by picking fights and whipping up resentment.

Both devolution and the Union work best, they argue, when the distinct roles and lines of authority between different institutions are clear. Tasking multiple executives with agreeing UK-wide policy not only undermines the proper function of the British Government but invites deadlock and dysfunction at the Union level, which will only strengthen the separatist case.

The Scottish Conservatives, they add, should know better than anybody that the Nationalists’ overriding priority is the dissolution of the UK. There are no serious grounds for thinking that they are suddenly operating in good faith on Section 11, any more than when they fall in behind Anna Soubry to fight for soft Brexit. They fight for that which best helps them dismantle this country.

Tomkins may eventually be proved right in his freebooting take on the importance of the Single Market’s rules. But Section 11 is not an eternal prohibition on devolution. It is designed to prevent important constitutional action being undertaken in haste which will be repented at leisure.

Yet it could fall. A number of Tory MPs would doubtless hazard the future health of the Union for the sake of a smoother Brexit and lose little sleep. The nationalists will denounce it and too many unionists, still apparently convinced that the key to defeating the SNP is giving them what they want, will support them.

If the Government truly believes that the constitutional implications of Brexit are as important as Section 11 suggests, it needs to make its case – and prepare for battle.