comment: >
  
  Rejoining the EU is pretty damn near a non-starter. For one thing, a major reason Labour didn't already go hard against Brexit is that they have enough Euroskeptic voters that it was as likely to hurt them as to help. 
  For another, the UK could never rejoin on their old terms, which were effectively a sweetheart deal. The EU honoured old opt-outs for the UK that allowed them to, for example, keep the pound. Those deals are void now and they have no reason whatsoever to offer them again. Especially since Brexit was arguably beneficial to the EU—it simultaneously removed the major country most likely to oppose further EU reforms and served as proof that leaving the EU is an immensely stupid decision. They have no reason whatsoever to let the UK back in with any concessions at all.
context: In the scenario you describes above, I think it is more likely that Labour would agree to attempt to turn the UK into a federal country rather than give SNP the referendum they want especially considering the polling on Scottish independence is still neck-and-neck and Labour definitely do not want to be held responsible for any potential breakup of the UK. On the other hand, I could also see Labour agreeing to the independence referendum and then working with the Tories to threaten Scotland with partition of its territory in the event the Yes side wins pointing to France's decision to partition Comoros and Canada's threat to partition Quebec as legal precedents.
  However, I highly doubt the scenario you are proposing will actually happen. Most of the recent polls show that Labour will win at least a comfortable majority in the next general election. Sure, a lot could change in the next 2 years but Keir Starmer has been working hard to repair Labour's image among voters by moving to the center and presenting himself as a viable alternative to the Tories. Starmer has purged Jeremy Corbyn and much of the far-left from the party while keeping MPs who still support Corbyn's reinstatement on the backbench.   The Labour Party Conference last September featured a tribute to the late Queen and an uninterrupted singing of God Save the King with the national flag on the background. Also, the Labour's position on immigration and asylum seekers is no longer different from that of the Tories. With all this, I am sure Labour is still very much on their way to a historic landslide victory. >
  
  Not sure the party has been making themselves a more appropriate choice vs the Tories with what is shown in the Labour conference last year (constantly having to reaffirm that anti-semitism is not allowed and being boo’d for it, female MPs being threatened into not showing up as seen with Rosie Duffield, claiming that capitalism won’t solve climate change but socialism will by some speaker). >
  
  Well the last point is accurate >
  
  I think now that Brexit is a more than a half decade old and all the nahnahnah-you-can't-regulate-us-anymore has been replaced by economic woes, I think there's just going to be a shift to Labour, who, instead of giving Scotland another referendum, might instead have a referendum about rejoining the EU. The SNP will back that.
  As for first-past the post, it sucks when a smaller group gets more power, but the UK situation is better than giving a bunch of land 40% of your senate.