Try the Transaction CSV Import add-on from Adept. It can do this.

Thanks Anita - I'll look into it. Do you use Adept yourself - would you be happy to share any good/bad points to help us make a decision?

Thank you for your help.

Hi Kaylee.  Yes I do use it regularly to import journals and bank payments. It's the only solution for us as we need to import the charity fund code which the inbuilt Sage import function won't do. But I'd recommend it anyway as it's significantly faster than Sage import and you can automate it if you want to, so it imports as soon as a file arrives in a pre-determined folder, then puts it into either a processed or faulty folder so you know what's been done.

I haven't needed the purchase import you are talking about, but have just starting using Adept's sales invoice importer, which does exactly as you say - importing several lines but linking them to a single header. Adept offer a 30 day free trial, limited to just a few lines to import, so it's well worth taking a look.

Great, thank you for your help, it's good to get the opinion of someone using the software 

Just a word of warning - when I tried to test the Adept importer in the practice company, it imported into live data.  Maybe there's a setting I should have changed (it is multi-company), but back up your real data first!