Forum Discussion
Thanks to both, first of all apologies for the delay (I should not post a question before a holiday) and secondly, I think the answer here was a mix of RTFM and me not paying attention.
I was able to get the import to do what I wanted (in this particular case import sites and allocate these sites to a customer and a project) using the RELATED CUSTOMER and RELATED PROJECT fields during import. The RTFM moment came about because I wasn't paying attention to the fact that I needed to use the record ID numeric value assigned to the customer and project already created.
A follow on question, if I changed the record ID field to the customer name and project name fields in those tables, am I able to use those fields to do the same import? Simpler than looking up the record ID for the appropriate customer or project in order to be able to import.