In reply to Anniebach; if one has made a will appointing executors they have a right to dispose of the body. It is generally agreed they should "have regard to any expression of wishes made by the deceased, but are not bound by them" (Buchanan v Milton [199]). I usually explain to Will clients that executors cannot be bound by funeral wishes because a) the Will may not be found until after the funeral has taken place and, b) they will be in no position to sue!
If there is no Will there is a hierarchy of who can take possession of the body; persons with parental responsibility for a deceased minor child, then a surviving spouse or civil partner (but NOT a "common law" husband or wife), then children (or their issue if predeceased), then parents, then siblings, then remoter relatives.
If there is a medical reason for it, a householder (or hospital) can dispose of any body on their premises, subject to the claims of those above. If there is a dispute about who has first claim, the person with possession of the body can make arrangements.
If no one claims the body the local authority has to dispose of it.