Cutting the new Part FCL licence invalidates it.
The CAA have issued specific instructions that state it must not be cut. It folds up to fit perfectly in one of the pockets. So does the medical. My examiner authority does the same along with the additional pages for it. The CAA also supply additional revalidation sheets that are the correct size to go in. By the time that lot goes in there is little room left. That's the reason there are so many empty pages. Think yourself lucky, most European countries issue the bit of paper in a single clear plastic pocket sized for the folded licence. At least the UK gave you one with room to expand.
It even fits perfectly my FAA Class 1 and Certificate.....