Hi Tom,
I think what you may be after is more of the project tagging, so you could tag an invoice, purchase, credit note etc to a ‘project’, which will allow you to view reports (profit and loss for example), and view anything tagged to it.
I’d recommend having a look at this thread which explains this feature in more detail:
http://community.quickfile.co.uk/t/projects-in-quick-file/1591
Hope that helps!