Bruce Anderson’s article was commissioned by The London Magazine in response to the recent Scottish referendum.

There is a good old Scottish word: thrawn. It is almost onomatopoeic. The accepted translation into English English is ‘stubborn’, but that does not come close to doing justice to thrawn. Thrawn to stubborn is like the difference between a gnarled, weathered, battered old oak tree and a rose bush. There is a Scottish politician and former MP called Tam Dalyell – Sir Tam, actually, but he will not use his baronetcy – who is the Platonic idea of thrawnness. The surname is pronounced Dee-ell. Over the years, it has often been commented on that this is not far from deil, the Scots word for the devil. In the 1670s, an ancestor, Bluidy Tam Dalyell, first raised the Royal Scots Greys in order to hunt down Covenanters. His descendant was equally bull-dogged in pursuit of his objectives.

Because it has never been written down, the British constitution is admirably flexible. Bits can be spatchcocked on to it in the most devil-may-care fashion. Thus it was with Scottish devolution, when the then Labour government first tried to implement it in the 1970s. That was not nearly rigorous enough for Tam Dalyell. He pointed out a serious problem. As the MP for West Lothian, he would have no say in education policy in Scotland if devolution were implemented. But he and his constituents would at least be able to vote for members of the Scottish Parliament. Yet at the same time, he would be able to vote on education policy in England, even though his constituents would be unaffected. This violated an essential principle of Parliamentary sovereignty, equity, accountability and responsibility. Normally, whenever MPs vote for a measure, it will affect their own constituents, who can hold them to account. In the case of Scottish MPs post-devolution, their votes on purely English matters would be irresponsible. That was grossly unfair.

When Tam sat down, another great Parliamentarian took up his point. Enoch Powell christened it the West Lothian question. That term entered the political lexicon and no-one has yet found a way forward. When he was Lord Chancellor and being harassed on the matter, Derry Irvine once said that the answer to the West Lothian question was to stop asking it. That was a spasm of exasperation, not a solution. No-one has taken any notice.

Thus far, the difficulty has been containable. At almost every election since Tam Dalyell raised his objection, the incoming government – or coalition – has enjoyed a healthy majority. The exception was John Major in 1992, but his administration was sabotaged by Europe and by his own party; West Lothian played no part. If David Cameron were to win an overall majority in 2015 – despite Europe and his own party – it would almost certainly be a small one. Equally, ‘devo-max’ would give even greater powers to the Scottish Parliament and thus add to the West Lothian conundrum.

At present, the Tories have one Westminster seat in Scotland and a substantial majority in England. It is easy to imagine a Tory government trying to enact an education bill which would only apply to England. There would be no problem in winning a sizeable majority among English MPs, but depending on the Parliamentary arithmetic, Scottish MPs could sabotage it – even though it did not apply in their constituencies.

In their approach to the Scottish referendum, English Tories displayed an almost unprecedented degree of idealism, beseeching the Scots to stay British even though this would make it much harder for Tories to win elections. But idealism has its limits. If the failure to answer the West Lothian question leads to lead to constant sabotage of English wishes by Scottish votes, there will be trouble.

To Unionists, this is all a source of sadness. In 1707, at the Union of the Parliaments, Scotland was a poor, backward and divided country on the fringes of Europe. Within a few decades, the Scottish Enlightenment was at the leading edge of European thought, while the glorious architecture of the New Town in Edinburgh was a splendid example of urban civilisation. Within a few more decades, the Scots were playing a prominent role in the Industrial Revolution and in the British empire.

These days, it may be that equivalent triumphs are harder to achieve. Even so, the Union has been one of the greatest constitutional successes in human history, rivalled only by the United States of America.