According to the section 41 of the Births and Deaths Registration Act 1953, disposal means “by burial, cremation or any other means”.
This raises the question: by what other means? There is presently no conventional alternative to burial or cremation in the UK, but in the US some disposals are carried out by means of alkaline hydrolysis (also known as biocremation, resomation, flameless cremation or water cremation). Legislation would need to be passed before this method is available in the UK.
A process involving the pulverising of a freeze-dried corpse was announced, but no successful trial has been known to have taken place and the process seems still to be at the concept stage.