Forgive my ignorance: how many airworthy Mk.XVIIIs are there, worldwide?

Two, soon to be three with any luck!

SM845

Now owned by Richard Lake, and based at Humberside Airport and sometimes Duxford.

SM969

??

TP280

Recently purchased by the Hanger 10 Collection in Germany, and currently with Meier Motors being returned to airworthy condition.

I believe there maybe another project that’s a candidate for restoration to fly also, TP276.

It will of course be interesting to see who the new owner of SM969 is!

Cheers

Paul