In my experience, the final degree classification of top up degrees is based 100% on the Level 6 top up year.
This is something that should be spelled out in induction week.
Module values vary. For example, final projects are usually 40 or 60 credits.
Your typical module is 20 credits.
You'll probably have a mix.
The regs usually dictate that you can't do more than 60 credits in a semester (to prevent overloading).
PS I've just had a look at the academic regs for Derby Uni and found the following, which I think confirms that your degree classification will be based on your L6 work alone.
Section F14.2
Determination of Honours classification following Direct Entry or entry with Advanced Standing
(i) If the mark average for the penultimate level cannot be calculated, e.g. because the student was a direct entry to the final stage or the student studied abroad for the whole of stage 2, the mark average for the final level will serve as the overall performance indicator.