The message
from "The3rd Earl Of Derby" contains these words:

If you want to buy some, they're a couple of quid each at my local
dump - any size, often half-full.

And this why Calor/filling stations charge a deposit because they're ending
up in a scrap metal yard.

ISTM that you have that the wrong way round. Calor gas bottles got
dumped because Calor agents would only give a refund if the original
invoice showing the amount of the original deposit was produced.

--
Roger Chapman