Looking at past papers is a very good idea for exams and part of being good at them. My sons are not reading law but at least one will study law from the Autumn (if he gets that 2/1 he needs for his post grad course) so they have timed essays allowing 48 hours or 72 hours for their 1 (or in the other case 2) exams. I see that their university Bristol also has online exams presumably for other subjects and that requires the students to sign an honesty statement. I don't know what that says.
I believe for exams some universities are doing an on line sweep of the room for each student to check on one is in the room etc who might be feeding in answers. Hopefully enough students are honest that things end up being okay.
They certainly should make it very clear what is allowed for on line exams so everyone knows where they stand. I presumed it would be like if you have a clash of A level exams where you know the questions early and are supervised by a parent or teacher until everyone else has done the exam so you don't tell anyone else the question or else that online exams were being done all at the same time (rather than on line essays you can answer over several days in place of an exam which are a different thing).
Perhaps students have their own internal conscience which will help them decide what might be bad and what is not.
It is just about never cheating to look at past papers however and anyone who is doing any kind of exam from the 11+ upwards would be silly not to look at past papers for months before their exam.