Isnt this some kind of suicide?

presumably you are talking about jehovahs witnesses or christain scientists here. Legally in the UK, it is only suicide if a person intentionally commits an act with the intention of killing themselves. It is not suicide if a person refuses treatment for whatever reason. In some jurisdictions courts have ruled that parents refusing to allow their children treatment on such grounds would be manslaughter, but I dont think this is the case in the UK