Thanks for the replies. Looking every few days since early 2019, I have only seen a handful of Y Reg hatchbacks or Aerodecks ever advertised.
By coincidence I passed a small independent used car seller just outside London today. This is the type of place with around 10-15 cars stored outside with a small workshop at one side of the yard. Being a Sunday it was closed.
I noticed that there was a blue R Reg hatchback in there visible through the fence. From looking up the Reg it has apparently done only 15,000 miles from new. They didn't have any kind of price displayed on it and the place doesn't appear to have any internet presence.