Thursday’s elections are likely to put more strain on the bonds holding the UK together

Tomorrow’s elections are of national importance because they are likely to put the integrity of the United Kingdom under further strain. In Scotland, the Scottish National Party is not expected to do particularly well in elections for local councils. Professor Stephen Fisher of Oxford University forecasts a net loss for the SNP of 24 seats, but the party remains so dominant in Scottish politics that this is only a minor correction.

Meanwhile, in Northern Ireland, the elections could have a much greater impact on the future of the UK. Sinn Fein, which wants a united Ireland, is likely to be the largest party and hence to have the right to nominate the first minister, while the Democratic Unionist Party will be entitled to nominate the deputy first minister – the reverse of the current arrangement.

The DUP will not do as badly as some of the reporting of opinion polls suggests, because the elections use a proportional system of voting in order of preference. Although the DUP is trailing Sinn Fein badly in first preference votes, it will pick up seats through transfers from supporters of other unionist parties. But it is unlikely to win more seats than Sinn Fein, and a Sinn Fein victory will only deepen the constitutional crisis already engulfing Northern Ireland.

The DUP has already put the devolved government into suspended animation with Paul Givan’s resignation as first minister, which meant that Michelle O’Neill of Sinn Fein ceased to be deputy first minister, as the two posts are tied to each other. That suspension is likely to continue, because the DUP is expected to refuse to nominate a deputy first minister, which would similarly prevent O’Neill taking the first minister post. Not that the DUP has any actual reasons for refusing except as a spoiler tactic to prevent Northern Ireland’s government from operating effectively.

As long as there is no first minister and deputy, the existing ministers carry on in caretaker roles, but are not allowed to make decisions that are “significant, controversial and cross-cutting”. The DUP’s aim seems to be to use the suspension to put pressure on the UK government to secure changes to the Northern Ireland protocol of the Brexit deal, which would then restore the popularity it would need to win another election.

It doesn’t sound like a great plan, but the party has run out of options, having made a series of bad decisions about Brexit. Whatever you think of its support for leaving the EU, it has taken a couple of wrong turnings since, opposing Theresa May’s compromise, which would have avoided a customs border in the Irish Sea, and believing that Boris Johnson had a workable alternative.

These mistakes have magnified the effect of Brexit on the unity of the UK. Just as Scotland voted to stay in the EU, so did Northern Ireland, and keeping an open border with the Republic of Ireland has tilted the north towards the south. The DUP objects to Johnson’s protocol because it has diverted trade from east-west, with the rest of the UK, to north-south, with the Republic, but partly that was an inevitable consequence of any kind of Brexit.

Combine that with Sinn Fein’s electoral advance and you can see why unionists are worried, however self-inflicted their woes. That is why thoughtful Conservatives say they are more worried about the UK losing Northern Ireland than Scotland.

These fears may be overdone in both cases. Sinn Fein is not that successful in Northern Ireland. It is unlikely to increase its share of the vote since the last assembly elections five years ago – its success is more the product of unionist divisions than of great enthusiasm for a united Ireland. Indeed, opinion in Northern Ireland remains consistently in favour of remaining part of the UK. The most consistently overlooked segment of Northern Irish opinion is Roman Catholic unionists.

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It is also worth remembering that opinion in the Republic is opposed to a united Ireland if it involves higher taxes (which it would – national income per person is much higher in the Republic).

What is also true, though, is that Scotland’s breakaway from the UK is less likely than Nicola Sturgeon would like. It was significant that this week she admitted: “I wouldn’t want to go ahead with a referendum that wasn’t legal.” In that case, she won’t be going ahead with another referendum, because it is clear that the power to hold one lies with the UK government, which may be why she is reluctant to publish the legal advice she has received.

And Boris Johnson has worked out that all he has to say to any request for another referendum is: “Not yet.” Unless support for independence becomes overwhelming, he can keep that up for ever, or until he ceases to be prime minister, whichever comes sooner.

Even so, English Toryism and hard Brexitism will always act as centrifugal forces on the union. The best argument for Scottish independence is to get away from English Tory rule; and the best argument for a united Ireland is to fix the Brexit border problem. The best chance of keeping Scotland and Northern Ireland in the UK in the longer run, therefore, would be a Labour government at Westminster.