Thank you for your quick response.
Yes, that does seem to be what I was asking for. However, I’ve had a go with it and I don’t think that we will be able to use it.
The categories are selected by checkboxes on the post screen, and we are expecting to have over 6000 of these, so it would not be practical to have a list of checkboxes this long. (our groups are cooking clubs in schools all over the uk).
I think we are going to come up against this kind of problem with a lot of plugins that I’m trying out.