We have to pay £350ish pounds for every year beyond year 3. So, you pay for year 4, and for any other subsequent years if needed. If you submit within 3 years 3 months, they refund the fee, but otherwise you have to pay.
I also have to pay an extra £350 when I submit because I'm having a second external examiner. I have to have two externals because I am staff as well as a student and there is no one here who is impartial enough to examine my work without needing to declare a conflict of interest. Super annoying.