[Koha] How to import loans data into Koha?

Gentle Reader, We are migrating records from a few small community libraries (currently held as a fancy spreadsheet) into Koha 17.05. I have figured out how to migrate the biblio records, items and patron data but I was wondering if there is a way to import data on current issues (loans)? All we really need to import is the item ID, the patron ID and the due-back date. Is there a tool to do this? Or is it a question of populating the issues table directly? If so, does anyone have a script to do this? Any pointers gratefully received ... Chris Brown