I suspect that the fee is the one charged by the CAA in place of the old C of A renewal fee.
It was quite a neat trick by the CAA to get the maintenance companys to do all the aircraft paperwork under the new part M that was once the responsability of the CAA for C of A renewal but to still keep charging the aircraft owners for the "service" allbeit with a name change!
As usual non of the money stays in GA !