It's a very thoughtful piece by a writer who has spent a long time in England, and I strongly recommend reading the whole thing.
Here are a few bits that struck a chord with me:
[The British] state has stopped England from pursuing its main mission, namely to build a inclusive, post-imperial, multi-racial society, by forcing it to engage with the totally irrelevant (from an English perspective) distractions of Scotland, Wales and Northern Ireland. From the viewpoint of the Scots, it has foisted thirty-five years of a destructive neo-liberalism upon us, and prevented us from becoming the European social democracy we are politically inclined to be.
The idea of the political independence of England and Scotland leading to conflict, hatred and distrust is the mindset of opportunistic status-quo fearmongers and gloomy nationalist fantasists stuck in a Bannockburn-Culloden timewarp, and deeply insulting to the people of both countries. Swedes, Norwegians and Danes remain on amicable terms; they trade, co-operate and visit each other socially any time they like. They don’t need a pompous, blustering state called Scandinavia, informing them from Stockholm how wonderful they all are, but (kind of) only really meaning Sweden.
The Union Jack is the increasingly shrinking fig leaf that strives to cover the growth of an English nationalism and consciousness, which is visible in almost every aspect of life in these islands over the last thirty years. And that, in a post-imperial world, is how it should be, and probably how it has to be. The problem that the Scots, Welsh and Northern Irish have to face, is that they have no place at this party, and neither should they: it just isn’t a great deal to do with them.
It's a very powerful article, and even more so because Irvine Welsh knows England so well. As he concludes: "Better together? Yes, certainly, but better independent and free together."