Boris Johnson’s decrepit, dishonest government was hit by two devastating by-election defeats in different parts of England last week.

Labour retook Wakefield in Yorkshire, a seat it lost to the Conservatives in the 2019 general election. More dramatically, the Liberal Democrats took Tiverton and Honiton, a seat that had been Tory since the dinosaurs were young. (OK, slight exaggeration.) That Lib Dem success saw the biggest ever majority overturned in a British by-election.

The Tory defeat has led to a debate about the need (or not) for anti-Tory parties to agree a pact to ensure the progressive vote isn’t split, which traditionally means the Tories win despite the opposition winning more votes. Margaret Thatcher famously enjoyed big majorities because of this.

Sometimes it doesn’t matter. Labour won a landslide in 1997 and 2001 under Tony Blair and the Lib Dems did well too. That was the reverse effect: anti-Tory voters teamed up to punish the Conservatives,

Could the same thing happen in 2024? Last week’s by-elections suggest it might. Tactical voting can work, especially when there isn’t a Jeremy Corbyn to deter Lib Dem voters or a Nick Clegg to deter Labour ones.

What about a repeat of the Tory tactics in 2015, saying Labour will be in the pocket of the Scottish National Party? I can’t see that having any traction in 2024. Boris Johnson is the greatest boost possible for the SNP. The SNP’s apparently unstoppable advance has been turbo-charged by the Tories and Brexit. Brexit is done, at least for now, but the return of a progressive UK government might be the union’s last hope. Especially if that government replaced the deeply undemocratic first-past-the-post voting system with some form of proportionate representation.

The progressive parties must state their case – their collective case – with confidence and brio. Take a leaf out of RMT leader Mick Lynch’s book – don’t let this battle be fought on a field chosen by the Tories. Britain – England, Wales and Scotland – must be better than this. Make the case for a fairer government that fights for all the people, especially those less well off, not just the privileged few who win every time with the Tories.

As a Welshman, I long believed that Wales was best served by being part of the UK. We are a small country that has traditionally looked east to our large neighbour England for trade and much more. Yet I have come to believe that the UK in its current form is a divisive, destructive influence. London doesn’t care (spicier epithets are available) about Wales. Or Scotland. Or Northern Ireland. Even worse, it will force any amount of destruction through that negligence, as Johnson’s poisonous rejection of his own agreement to the Northern Ireland protocol shows. The Tory embrace of Brexit has made our nations and their peoples poorer than they were before. How could Wales – or Scotland – do any worse alone than under destructive London rule?

The next five years will decide whether the UK has a future.