I think our university doesn’t class that as plagiarism but does consider it against the rules.
EDIT: found it in the handbook:
1. Assessment irregularities take various forms including:
a. plagiarism: Defined in General Regulation VIII Examinations C as unacknowledged use including quotation and close paraphrasing of other people’s writing and ideas, amounting to the presentation of other person’s writings or thoughts as one’s own. This includes using material which is available on the world-wide web and in any other electronic form, and “contract cheating” i.e. obtaining an essay from an essay writing site or equivalent source and submitting it for marking, as if it were your own work.
b. Multiple submission: the inappropriate submission of the same or substantially the same work of one’s own for summative assessment, in connection with an academic award.
Be slightly careful if you’re submitting things you’ve submitted before for marking to a Turnitin (or similar) system. We use Turnitin and it scans both online sources and also any work that has been submitted to Turnitin from other universities that use Turnitin. So if your previous work is already in a database somewhere it will flag as 100% copied and you might end up arousing unwanted interest in your submissions, which is a huge hassle even if it ends up not being against the rules.