Ian,
I know of three, all in my collection and all from very old collections,
https://forum.cartridgecollectors.org/t/british-hn-9x19mm-with-chalk-bullets/30666
Now you turn up two more. I suspect they were very short range practice cartridges, apparently loaded shortly after WWII or no earlier than 1944 from pulled down ball rounds or if done during the war using primed empty cases. All have a clear lacquer on the bullet so all were likely made by the same organization to the same “spec”. It is possible they were british military, or Territorial Army. I would love to know what powder they contained and how much, but can’t figure out a way to pull one apart without destroying it. I have never seen a BE one before.
I hope someone has some insights.
Cheers,
Lew