Christopher Key wrote:

[Loftbox]
This comes with a fairly heavy duty earth bonding terminal; should
this be connected back to the main equipotential bonding connector?
Instinctively, I would have assumed yes, in order to provide some
protection in the event of a lightning strike, and to keep any large
potentials from developing between exposed metalwork, e.g. radiators
and the aerial system.

If all the outlet points are serving a single household then the bonding
is optional. The main purpose of earth bonding an aerial system is to
ensure safety in a distribution system serving more than one household -
e.g. in case your neighbour decides to connect the coax to the mains
(this used to happen frequently in the days of live-chassis TV sets with
faulty aerial isolators). It is not a lightning protection measure -
that needs to be done outside the house, bonding the antenna system and
mast using much larger conductors. System earth bonding has
superseded the former practice of using isolated output plates, which
are a disaster EMC-wise, and don't pass LNB power/control, etc.

The earth bonding terminal should be connected to the main earth
terminal of your electrical installation with a min. conductor size of
4mm^2 (or 4mm^2 copper equivalent, if not copper). (The relevant
standard is BS EN 50083-1.)

However, I understand that some AV equipment is designed to leak to
earth slightly, and am concerned about this causing ground loops and hum.

That can happen, although doesn't seem to cause problems too often.
Most A/V equipment is Class 2 and doesn't have its own earth connection
to create a loop. Even if you don't earth-bond you'll still be
connecting the 'grounds' of various bits of equipment together via the
coax, into one floating mass, so to speak. If you do have a hum loop
problem the best solution is to fit a 'galvanic isolator' (aka
braid-breaker filter) on the antenna input of the affected equipment.
The isolator is available from companies like Teldis (but sit
comfortably when you ask the price!).

Any advice much appreciated.

HTH, HNY
--
Andy