As the House of Lords Constitution Committee pointed out in its short report on what was then the Scotland Bill in 2011, while the devolutionary principle of Home Rule has now been accepted, indeed embraced, by all three of the UK’s main political parties, the consequences of devolution for Whitehall and Westminster continue to be unresolved. For Government the key issue that remains open is the funding of devolution and, in particular, the future of the Barnett formula. For Parliament, the main ongoing tension concerns the age-old West Lothian Question.

This week has seen a potentially significant intervention on each of these matters. In a breakthrough speech delivered in Edinburgh on 26 March Ruth Davidson MSP, the leader of the Scottish Tories, said that the “much-derided and little understood” Barnett formula is in its “death throes as it stands”. Well, I’m not sure about that – I detect no appetite either in Government or Opposition for the Barnett formula to be revisited for the time being – although everyone knows that it will have to be looked at one day.

The UK Government established the McKay Commission in early 2012 with a brief to address the West Lothian Question (“WLQ”). The Commission published its report on 25 March. The WLQ, so named because it was one of Tam Dalyell’s favourite puzzles when he was MP for the West Lothian constituency in the 1970s, arises as a result of the asymmetrical nature of devolution in the UK. There is devolution in only three of the four nations of the UK: there is devolution in Scotland, Wales and Northern Ireland, but not in England. There is modest city-wide government in London and there is what remains of local government throughout the UK, but Labour’s attempt to introduce regional government in England was overwhelmingly rejected in a referendum held in the north-east of England in 2004 (the McKay Commission describe this result as a “swingeing rejection” (para 70)). No one suggests that regional government in England should be revisited.

Thus arises the following problem: health is a devolved matter in Scotland. Legislation concerning the NHS in Scotland is for Holyrood, not Westminster. MPs have no say over the health service in Scotland. Because there is no body in England to which responsibility for health is devolved, MPs do still have a say over the health service in England. And here’s the rub: all MPs do, whether they represent a seat in England, Scotland, Wales or Northern Ireland. Why should a Scottish MP be able to vote on legislation relating to the health service in England when an English MP has no vote on legislation relating to the health service in Scotland? That is the WLQ, and it arises not only with regard to health, of course, but with regard to any matter that is devolved in Scotland or Wales or Northern Ireland but not devolved in England.

Does it matter? Well, it might. The truth is that it does not matter in practice very often, but the evidence suggests that it is starting to matter rather a lot in terms of how the English perceive the fairness of the devolution settlement (and, in this respect, perceptions as to the unfairness to England of the Barnett formula are closely related). The extent to which Scots felt that their government was illegitimate in the 1980s and 1990s led to the Home Rule of the Scotland Act 1998. If English grievances about West Lothian and Barnett are not addressed – and sooner rather than later – we may yet see further seismic shifts in our constitutional arrangements, as significant for England (and the Union) as was the arrival in 1999 of devolution for Scotland (and the Union). The McKay Commission is right to encourage Government not to under-estimate the extent, or the potential importance, of English unease with aspects of the devolution settlement: as is reports on its opening page “Evidence suggests a significant level of grievance among the people of England, sparked by the perception that Scotland enjoys advantages relative to England under current governing arrangements ... There is a clear and enduring sense that England is materially disadvantaged relative to the other parts of the UK, especially Scotland” (para 6).

The Conservative party has been particularly concerned about seeking an answer to the WLQ, motivated perhaps by a fear that a closely fought election (such as the general election of 2010) could result in the Labour party having an overall majority of seats in the Commons without being the largest party in England. Remarkably, this has actually happened only very rarely and, even then, only for short periods of time (namely, 1964-66 and February-October 1974). None the less, it could happen and, if it did, the English might feel (as the Scots felt in the 1980s and 1990s) that they were being governed by a party they did not elect.

Relatedly, a government with an overall majority of seats both in England and in the UK might be able to push through legislation affecting England only, despite the legislation in question being supported by a minority of English MPs. This occurred twice in 2003-04 when considerable numbers of Labour MPs from English constituencies rebelled against their party whip on the creation of foundation hospitals and on the introduction of university top-up fees. Owing to devolution, neither of these policies applied to Scotland, yet both were pushed through only with the support of Scottish MPs. It must be said, as the McKay Commission were at pains to point out, that such occurrences are extremely rare.

The WLQ is not difficult to answer, logically. But it has become difficult, politically. Given that the WLQ arises because of the asymmetrical nature of our devolutionary arrangements, the logical answer rather obviously is to make our devolutionary arrangements symmetrical. But this solution has no political viability, given the rejection of regional government within England (see above) and the fact that there is no mainstream demand for an English Parliament. Even if there were such a demand, students of federalism tell us that a federal structure in which one component (England) comprises fully 85% of the whole (the UK) would be so imbalanced that it could not but fail. Admirably, the McKay Commission wastes no time pondering abstract solutions that stand no chance of being implemented (dreamers fixated on “devo-max”, take note!). The report is refreshingly realistic, noting that “it is in the nature of our unwritten constitution that constitutional change is generally likely to be effective only if it has [widespread] support and goes with the grain of political reality” (para 144).

Until the publication of the McKay Commission’s report, the most popular answer to the WLQ appeared to be some variant of the idea that “English votes” should determine the making of “English laws”. The argument tends to run as follows: the jurisdictional or territorial extent of each Bill introduced into Parliament is routinely provided for in terms. When the Bill applies only to England, or only to England-and-Wales, the legislative process in the House of Commons should be confined only to MPs representing seats in England, or England-and-Wales, as the case may be. The Speaker, suitably advised, could rule on any contested matters, as he rules now on whether a Bill is a Money Bill for the purposes of the Parliament Acts 1911-49. Bills certified by the Speaker to be England only Bills, or England-and-Wales only Bills, should undertake their passage through a House comprising only the MPs from English (or, as the case may be, English and Welsh) constituencies.

This solution suffers from several drawbacks, however. First, it creates two classes of MP. English MPs would be able to take part in all parliamentary proceedings, but Scottish, Northern Irish and Welsh MPs would not. Secondly, it is rather inelegant. Labour peer Lord Foulkes described it as “legislative hokey-cokey” and Conservative MP Sir Malcolm Rifkind dismissed it as “a nationalist solution to a unionist problem” (McKay Commission, para 148). And thirdly, it could pose insurmountable problems for the constitutional accountability of Government to Parliament. The political make-up of the House of Commons as a whole, of English-and-Welsh MPs, and of English MPs alone, could be different, and yet the Government of the day would need to be accountable to each. Depending on the electoral arithmetic, things could get extremely messy.

In a paper written by my colleague Jim Gallagher and published earlier this year by the IPPR a less problematic variant on this theme was proposed. Under Professor Gallagher’s scheme, England only Bills (or England-and-Wales Bills) would have their second and third readings on the floor of the House in normal way (i.e. with all MPs able to take part and vote) but their committee and report stages would be undertaken only by MPs from England (or England-and-Wales, as the case may be). Thus the votes in principle on Bills (at second and third reading) would be for the whole House, but the detailed scrutiny and debates on amendments would be only for MPs with English (or English-and-Welsh) seats.

The McKay Commission has built on this scheme, but has added to it a novel and rather clever twist. Their addition ingeniously borrows from the devolutionary arrangements that already exist for Scotland, Wales and Northern Ireland.

As a matter of strict law, the United Kingdom Parliament retains the power to legislate on matters that are devolved to the Scottish Parliament (Scotland Act 1998, s 28(7)). But as a matter of practice Westminster will not normally exercise this power without Holyrood’s consent: this is the famous Sewel convention, and the parliamentary apparatus of the legislative consent motion (“LCM”) enables the convention to be implemented in practice.

The McKay Commission has recommended that, for Bills that apply only to England or to England-and-Wales, the consent of English (or English-and-Welsh) MPs should be sought and obtained before the House of Commons may proceed with the Bill’s second reading. Such a practice should be written in to the procedures of the House of Commons. The full House would retain the legal right to legislate on English-only matters (as, under the Scotland Act, it retains the right to legislate on matters devolved to Holyrood) but in practice the exercise this right would become subject to the English MPs (or English-and-Welsh MPs) first signifying their consent.

In the view of the McKay Commission this approach would have the merit not only of mirroring for England what already occurs for Scotland, Wales and Northern Ireland, but it would also be rooted in principle: namely, the principle that “decisions at the United Kingdom level having a separate and distinct effect for a component part of the United Kingdom should normally be taken only with the consent of a majority of the elected representatives for that part of the United Kingdom” (McKay Commission, para 109).

Is this a constitutional convention? Not yet, clearly, because as things stand this principle does not apply to England. Should it become one? In the view of the McKay Commission it would be desirable if it did but, again refreshingly, the McKay Commission is smart enough to know that neither the Government nor the House of Commons can simply create a new constitutional convention by declaring one. In the Commission’s words, “A constitutional convention has to emerge from practice, and be established and confirmed by it over time. With usage, the general acceptance of the principle we have identified may well result in practices that have the status of a constitutional convention. We hope it does” (para 123). Bravo to that.

Adam Tomkins is the John Millar Professor of Public Law at the University of Glasgow