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Question 1. I have been examining my earth bonding and have found
that the earth connection between where the cable enters my house to
the other size of the main fuse is made from earth cable that is only
about 3mm thick at most and it is not insulated.

3mm dia is 7sq mm - ie actually stock size 6mm sq??

SFAIUI it may not need insulation - would depend on risk of incidental
physical damage.

Presumeably this is
fairly old. This is only a short length about 25cm. There is then a
copper covered cable that goes for about 6 metres to the meter. The
earth connection into the consumer unit and connected to the gas and
water is much more substantial and is insulated.

From your bare description this sounds inadequate but for me to make
useful observations you need to provide clearer information about your
installation eg

approx age; if possible the earthing system (TT/TN-C-S/PME/TN-C are
the most likely).

The earthing is TNS. i.e. supplied via the armoured cable coming in
from the street. This looks to be at least 30 years old.

This goes into the suppliers fusebox. The other side of the fusebox is
a a copper covered cable which goes to the meter.

The armoured cable and this copper covered cable are joined on the
outside to continue the earth. This is done with uncovered stranded
cable of about 3mm diameter.

--- -------------
============= Fuse ================ ------- to meter
---| |-------------
|----earth link-----|

TFT but hard to be definite without seeing the set up.

Some thoughts:

loooking at the sizes specified in OSG table 10A (pg161) a 6mm sq
earth might be possible in a small sized supply (or possibly was
once?). On balance unlikely though, so:

*Perhaps* is the supply fuse box steel? It also sounds as if the
ongoing cables are MICC (mineral insulated copper covered) cables.

If so that may be a partial explanation. *If* it is steel & the
incomer is SWA then the box via the clamps at the inlet & outlet could
be providing earth continuity. The 6mmsq link being to reinforce the
earthing.

From the meter the tails are connected to the consumer unit. The earth
connection

sorry - not following you here precisely - earth connection from
where?

into the consumer unit is 10mm diameter insulated cable.

if you mean this is the main earthing conductor from the supply, then
it could well be a tad too small - 16mmsq being more normal.

do you mean 10mmsq?

The earth is then connected to the gas and water pipes, again using
10mm insulated cable.

If so that appears to be correct for usual sized domestic
installations (same OSG table).

As far as I can tell this part appears to be fairly modern and appears
to be in line with my understanding of the regualations. It just seems
strange that the incoming earth by the fuse seems so inadequate.

Where does the supply companies responsibility end, is it at the fuse
or the meter. If at the meter, then I will be getting the electricity
company in to replace this.

(a) so far as the supply (other than earth is concerned), at the point
the tails leave the elec co fuse or cut-out (if you have one), SFAIUI.
The tails are yours & you have to supply them if you have a new or
upgraded installation.

(b) earthing SFAIUI is the consumer's responsibility, but for certain
supply specs (PME/TN-C-S & TN-S) the elec co has (again, SFAIUI) to
supply an earth point. The rest is yours to worry about.

One way forward may be to check that everything your side of the
supplied earthing point is hanky-dory then ask the elec co to check
their earthing as it looks old/decayed/inadequate/some other sob
reason. Check if they'll charge first, though.

HTH