From the other posts you have probably realised that your actions in
killing
this creature and putting down slug pellets was not the best option.

It does sound like the Elephant Hawk moth caterpillar, the moth itself is
one of the largest we have in the UK and the caterpillar is
correspondingly
large.

Please, please in future try to find out what you are dealing with before
you destroy it.
It really is not difficult to tell the difference between a slug and a
caterpillar.

If you can get yourself a book on common garden insects and animals and
get
to know what is what, you will find you will live much easier with the
creatures around you.
Best wishes
Tom

I agree it does look like the "Elephant Hawk Moth" caterpillar and if I had
known what it was at the time I would not have taken the action I did.

Working in this garden for 30 years I had never seen anything like it before
(of this size) so immediately thought it must be something (bad) bought on
by this years weather conditions.

Thanks to everyone for identifying it.

M.