Sorry about the long subject! :-)

I know (too much!?) about Part P but was wondering if the requirements
for someone who can issue site inspection certificates for caravan
site electrics are the same, or more stringent, or what?

This is the certificate required for 'Certificated' sites which are
sites approved by the Caravan Club or the Camping and Caravanning
Club (and some others now I believe) for up to five caravans. These
often provide electrical hook-ups via what in french are called
'bornes', not sure what they are in english. These sites need an
annually renewed inspection certificate for their electrics.

--
Chris Green