You can only own human bones without a licence if they are strictly for your personal collection and stored as part of your personal collection and not on public display.
Because the skulls & bones contain human cells they fall into the category of 'relevant material' within the Human Tissue Act and the following rules should be followed:
Human skulls and bones should be treated with dignity & respect. They should never be put on public display without the appropriate licence and should never be used for transplantation purposes or for any of the scheduled purposes listed by the Human Tissue Authority (for example research, post mortem, anatomical examination, teaching or public display.