We don’t know what’s going to happen in today’s Stoke by-election. Nonetheless, we do know that Gareth Snell, the Labour candidate, has played the England card.

In doing so he’s actually keeping faith with his predecessor – Tristram Hunt was a high-profile advocate of an English Parliament, surely one of the worst ideas in British politics – and matching other Labour candidates such as Sion Simon, the party’s candidates for the West Midlands mayoralty, found here thundering “This is England” on a leaflet denouncing “London politicians”.

Snell’s use of the St George’s Cross has prompted predictable handwringing from progressive sorts who think it racist, and counter-wringing from Blue Labour types who insist that Labour’s future lies in harnessing English nationalism.

Both sides are wrong. Using the English flag, and trying to tap into an English identity, isn’t racist. But it is spectacularly short-sighted, and suggests an almost wilful refusal on the part of some in English Labour to learn the lessons that are being taught, very painfully, to their Scottish and Welsh comrades.

Nationalism is not a winning vehicle for social democrats. It’s possible to ride that tiger for a while, even to the point of temporary political hegemony, but in the end it will buck you off and eat you, before which more and more of your energy will be focused on just clinging on.

Consider Scotland. Labour first started “othering” the Conservatives in the mid-Eighties, delegitimising British general election results in the process. This was indisputably a tactical success: the Tories were boxed out of the political conversation north of the border, and Labour secured an extremely dominant position for several decades.

Yet now the party’s position lies in ruins, and the Scottish Parliament is split between a populist SNP government and a Tory opposition. Neither Labour, nor the sort of politics Labour is supposed to represent, has prospered.

Turning politics into a “who’s the most Scottish” competition worked when Labour were facing off against the Conservatives but left the party exposed against actual nationalists, who can always afford to cleave to popular sentiment more completely than any party built around a wider philosophy.

Meanwhile political debate in Scotland may be couched in the language of progressivism, but as others have pointed out the key driver is more often difference from England. Failing policies are draped in the national flag, and devolved politicians treat attacks on their record as a slight against the nation.

Thus the SNP can command strong support amongst working-class Scots even whilst implementing policies which prioritise giveaways to the well-to-do, such as abolishing tuition fees and prescription charges.

And this isn’t just a peril that looms when capital-N nationalists take power, either: once political debate turns down this avenue nationalism seeps into other parties too.

Welsh Labour provides a clear illustration of this process in action. For example Huw Lewis, then Cardiff’s minister for education and skills, denounced Michael Gove for harbouring “indestructible colonial attitudes” after he had the temerity to compare Wales’ educational outcomes with those of England.

(It’s not hard to see why Lewis might be sensitive on the subject: as in Scotland, local Labour politicians used devolution to opt out of and even roll back the public service reform agenda, and oversaw a collapse in standards as a result.)

Or there’s Leighton Andrews, another former education and skills minister, declaring the UK Labour leadership contest – in which Welsh members had a vote like everybody else – as an “English Labour” issue.

At its best devolution offers an opportunity to compare different approaches and pool experience across the UK. Nationalism short-circuits this process by giving politicians whose policies are failing both the means and the incentive to shield them from unflattering comparisons.

Even when it stops being tactically helpful, this sort of thinking can prove an addictive habit – read David Taylor, a Labour supporter and former special adviser, explaining after the general election how Welsh Labour’s fixation on the Plaid Cymru left it ill-prepared to face a resurgent Conservative Party.

This, rather than overblown fears about racism, is why Labour needs to stop trying to find short-cuts to dominance – or even to relevance – by inflaming nationalist sentiment. It might win battles in the short term, but both Labour and social democratic politics in general will be the losers in the end.