robgraham wrote:

The earthing terminology doesn't mean anything to me

http://www.diyfaq.org.uk/electrical/...al.html#system

but the overhead feed to the house is two wire and there's a
none-to-heavy green and yellow wire coming out of the meter box and
disappearing into the ground - the house was re-wired about 25 years
ago I think.

Well that sounds as if it's TT. The wire you mention will go to an
earth electrode - usually a buried rod.

The floor in both the initial small brick shed and in the wooden garage
is concrete. Neither floor is damp and certainly the garage one has a
dpc. The electrical equipment I referred to is all in the garage.

No metal pipes anywhere.

No RCD's

Oo-err. No RCDs anywhere? Not even a whole-house 30 mA RCD, or
possibly an older 30 mA earth leakage circuit breaker (ELCB) between the
meter and the consumer unit, as would have been common practice when
this was wired.

Concern - well it was something to do with earthing on long cable runs,
and your comment about pre 1984 cable might back that up.

Your advice would be appreciated.

If the earthing is TT (i.e. with no metallic earth path back to the
supply distribution transformer) and there is no form of residual
current or earth-leakage device anywhere in the installation then there
is certainly a very dangerous situation since it's highly likely that
any earth fault would not be cleared (not enough current to blow the
fuse) leaving exposed metalwork live. (In the jargon this is called
risk of electric shock through indirect contact.)

Obviously, detailed advice can't be given without seeing the
installation. If you are worried, and from what you've said there may
be grounds to be, then I suggest getting a competent electrician
(someone with a C&G 2391 certificate in inspection and testing) to do a
Periodic Inspection. Done properly this will give your dad a
comprehensive report on the condition of the installation, with
recommendations for remedial work.

Remedial work, if it is TT, is likely to involve providing 100 mA RCD
protection for the whole installation, together with 30 mA RCD
protection for all socket-outlets on (at least) the ground floor and in
the outbuildings. Another option might be to have the overhead supply
upgraded to PME (TN-C-S) in which case the 100 mA RCD would not be required.

--
Andy