From The Lancet:

An intense debate has been rekindled in orthodox Jewish circles on whether brain-stem death is compatible with the definition of death by the Halacha—the collective body of Jewish law. Last week, the UK’s Chief Rabbi Jonathan Sacks caused widespread consternation among physicians when he issued an edict stating that he and his rabbinical court—the London Beth Din—reject the legal and medical definition of death and only accept the traditional halachic definition of cardiorespiratory failure. This apparently regressive interpretation comes at a time when all countries are discussing the most effective ways of encouraging organ donation in an attempt to deal with growing waiting lists for transplantation.