Search google for trade direct insurance, mine was around £100 including £1000 of tool cover.
(I don't have or need indemnity insurance though).
Ill be interested to see the replies regarding LTD, as I am also considering it at the moment.
The 9.5kw was incorrect on a 32a breaker too.
I very much doubt you will be able to take a used shower back to the store!
A 45a breaker on a 4/6mm cable will result in a fire.
Unfortunately its not quite as easy as that, you may be better off just buying a class 2 double insulated light fitting.
Is there no earths at any point of your lighting circuit?