Parliament is completely sovereign. It can overturn laws, never mind decisions based on interpreting laws. UK parliament has even made lots of ex post facto laws over the centuries. It's one of the fundamental disagreements, along with taxes, that led to the foundation of the United States.

Here's one example: Alan Turing was convicted of "gross indecency" (having gay sex) and ultimately took his life rather than live with the chemical castration ordered by the courts. It took a lot of convincing, but in 2017 Parliament ultimately passed a law pardoning all men convicted of that former crime. It doesn't matter how correctly the court interpreted the law in 1952, it was fundamentally a miscarriage of justice that we recognise in the present day.

It has already been determined by other court cases that many of the court cases that convicted SPMs were unsound, particularly because the court took the Post Office's word for it that their software worked correctly, and we know it did not. Rather than wait years to thoroughly re-examine every case on its merits, which would in itself deny justice to anyone who dies of old age in the process, we should move forward by annulling all of the Post Office's cases.

We don't have a constitution, you mean a change of legal precedent. I agree that's its and awful precedent to set. But it's already been done with Parliament declaring Rwanda safe, changing convictions doesn't seem so beyond the pale. I'm honestly not sure what else to do about it though. The sheer scale of incompetence and cover up in the post office and the software company will likely take years to sort through. Can the victims really wait that long? What is the alternative? Having everyone convicted file an appeal? After everything they've already gone through? Frankly, just wiping the slate clean and getting rid of all the convictions seem like the good move to me.

Given that we clearly had an exhaustive list of all of these miscarriages of justice, I too would have preferred that we fixed our absolutely shambolic and chronically underfunded court system to process the backlog properly. But given that is unlikely to happen in this or presumably the next parliament, quashing the convictions seems like an acceptable outcome. And we only just passed a law saying "Rwanda is a safe country because it is a safe country" to route around the legal system, this stuff is hardly unprecedented.

Prior art; Alan Turing law, Policing and Crime Act 2017

https://en.wikipedia.org/wiki/Alan_Turing_law

Although, I don't see why the courts themselves could not overturn all cases that included evidence from the accounting system in question.