There is on an odd collection of circuits with one single
socket on its own circuit!

It is normal to have a dedicated circuit without RCD protection for the
fridge/freezer. This ensures that an earth RCD trip elsewhere in the house
doesn't ruin all your food.

Also, there is no earth in the lighting circuits and there appears to
be no earth bonding for any of the metal objects in the house,
including the sink next to the dish washer.

The kitchen sink does not need to be bonded. Indeed, it is better to
insulate it by using plastic supply pipes if possible. That way, it doesn't
act as an earth, so you don't get a shock through it.

This will have to be rectified as I have recently purchased
an electric shower.

Yes, you should install supplementary bonding in the bathroom. However,
again it is safer to use plastic pipework. If all plastic pipework is used,
then the baths and radiators don't need bonding either. The electric shower
DOES need cross bonding.

I thought there was a problem with the RCD as several times it has
tripped when I was doing work to individual circuits. I had assumed
that as I had popped the circuit breaker for the circuit then that
ciruit was comletely "dead".

Nope. The MCBs do not fully isolate the circuit, they just cut the power.
Personally, I always isolate the whole thing at the main switch (unless it
is an DP RCBO circuit, but these are rare).

now understand that, if you short the earth and neutral then the RCD
will trip. I stand to be corrected!

Prepare to be corrected! Depending on the type of your earthing
arrangements, a neutral/earth short is unlikely to draw enough current to
blow the RCD. However, it may provide a sneaky backdoor for the neutral
current from a different RCD protected circuit to bypass the RCD and set it
off. Such an effect may be dependent on the current usage of that circuit
and might only manifest when a beefy appliance is turned on.

I can't recall whether there were any other appliances running at the
time although I dont think there were. As to the "shock" it was more
of a jolt. The machine was not actually on at the time.

It could easily just be a faulty earth, rather than a more serious fault.
Obviously, it must be fixed.

Christian.