Guy King wrote:
The message .com
from "Redeye" contains these words:

i've come to the conclusion that i've followed bad advice which is
probably the cause of the problem. i'd also been warned not to
overtighten compression joints, but advice here seems to suggest that
isn't possible.

Well, it is if you're a gorilla...

Or it's 8mm pipe.
With 22mm compression fittings, you'll have a job breaking the fitting
so that it won't seal by overtightening.
It's probably possible, but you'll need a long spanner, and the pipe to
be restrained quite securely.