I recently had a new boiler fitted in my house. One thing that the
installers didn't do was "ME Bonding". I understand this is something to do
with earthing any metal pipework that comes from outside the house (in this
case, there is a gas supply pipe and a pipe which I believe is the emergency
drain or something similar). Is this correct, and if so, how do I go about
doing it?

Thanks in advance,
Jon