G.W. Walker wrote:
...how do you stop compression fittings from leaking? I
plumbed in some new stuff at the weekend, but lots of the
joints are now leaking.

You may not have tightened them enough, undo one and look
at the olive. It should have squeezed into the pipe by a
small amount, enough so that it's tight on the tube but
not excessively sunk into it, or deformed. If you have not
done them up enough, do them up a little more until they
don't leak! If you've over-tightened them, they're scrap.


I resisted using PTFE tape on
every single joint, but is that the answer? PTFE wrapped
around every olive..?

You should not use PTFE tape or anything else on these
joints.