> Our supreme court is young (est 2006 or so)
This is not the case at all. The "Supreme Court" in the UK is the latest version of the UK's "court of last resort". Previous to this it was the House of Lords one would appeal to (it had functions to sit as UK's top court as well as the 2nd chamber). The House Of Lords was the Court of last resort for the UK since at least the 1800s.
From the Wikipedia page on the "new" UK supreme court:
"It assumed the judicial functions of the House of Lords, which had been exercised by the Lords of Appeal in Ordinary (commonly called "Law Lords"), the 12 judges appointed as members of the House of Lords to carry out its judicial business as the Appellate Committee of the House of Lords."
Indeed, the first 12 justices on the "new" supreme court where just the exact same 12 Law Lords from the previous House of Lords system.
The 2006 "Supreme Court" rebrand was a continuing reform of the existing system, not some new level of appellate court the UK had never had before. In reality, they both perform the same top appellate court/court of last resort role. You could bring the same types of cases to the House of Lords as you can to the Supreme Court, and the Law Lords presided over many of the UK's most significant constitutional cases.
There are various political reasons why this "rebrand" to Supreme Court was done, but I've typed enough and can't be bothered delving further into this in a reply. It's fundamentally a continuation of the previous long standing Court, and precedent from the many, many pre-existing HoL Court decisions is equal in power to that of the Supreme Court's decisions.
Had Gina Miller's case been say 10-15 years earlier, the HoL would have heard and decided the case too - she did not need the existence of a "new" "Supreme Court".
> https://en.wikipedia.org/wiki/Judicial_functions_of_the_Hous...
> https://www.parliament.uk/about/mps-and-lords/about-lords/lo...