Software that old generally requires old hardware to run on (at least spec. wise). The company I work for was recently involved in writing a replacement for just such an old (and business critical) system a client had. The main driver was that it was becoming increasingly difficult to source replacement hardware to run the old code on.

TBH I don't reckon there's much to choose. I was with Yorkshire all my life until 2010. They really let me down (won't go into details) but suffice it to say we wrote twice to them to complain and were ignored. We only go a response when we switched banks.
Their current TV ad campaign is laughable but not funny.

Not if its a Tandem (as was) now HP NonStop server type of machine. You can run software decades old on that which was written when they were 16 bit machines classed as mini-computers. Most banks rely on these machines and the software. Lloyds, Barclays's, Nat West, HSBC, ING and various others all have big investments in this little known hardware.

Having spoken with their IT guys all last week (until they introduced Business Incident Managers to fend the calls) I'd say that if that was the case then no one told them!

"Aaaaaaaaaaaannnnd - always look on the bright side of life..."