The book of Leviticus instructs us “Do not stand idly by the blood of your neighbour” (19:16) and tradition takes this obligation so seriously that we find this mitzvah extended from being obligated to save life to being duty bound to hire others if necessary in order to help us (Sefer Hachinuch 237). The mitzvah applies everywhere at every time, is an obligation for both men and women and we know it as pikuach nefesh, the duty to save life.

Pikuach nefesh overrides almost all other mitzvot, and is the basis on which organ donation is not only permitted but even expected by many halachists.

On the whole, halachic debate has centred on what defines death: the cessation of the heartbeat or brain-stem inactivity. Medical opinion uses brain-stem death rather than cardio-respiratory death as the critical criterion, and this opens us to the possibility of being able to give many more organs and hence save many more lives. For those who choose to define death as lack of heartbeat and breath, it is still possible to donate certain organs and tissue.

All this is reasonably uncontroversial — the beliefs that Jewish bodies must not be subject to medical intervention post-mortem, or that we must be buried intact in order to be fully resurrected are not supported in classical Jewish texts. And certainly the mitzvah of pikuach nefesh would take precedence in these cases. So we Jews should be carrying a donor card, and there are even some (from www.hods.org) which declare which definition of death we would like to have used.

To fulfil any mitzvah, we have to be mindful of what we are doing. To fulfil the mitzvah of pikuach nefesh we should make known our wish to donate our organs post-mortem. Organs donated on our behalf or with our consent assumed are not our mitzvot per se. And this leads us to the problem of presumed consent which has recently been legislated for in Wales and which is being considered in other parts of the UK: instead of a person indicating their consent for their organs to be used by carrying a donor card, for example, doctors would assume that the organs can be taken for use unless the person had indicated objections during their lifetime.

At first glance, it seems to be an elegant solution to the lack of consented organ donations: to assume that people would want a good outcome for others rather than to assume that they would not unless they specified so. But a more detailed look raises a forest of ethical problems and challenges principles on which our society is organised.

Medical ethics committees use three golden rules: firstly, any medical treatment should be therapeutic where possible, and at the very least do no harm to the person. Secondly, the person should understand what is to happen and give explicit consent. And thirdly the intervention must be based on good science and be expected to work.

While taking the healthy organs from a dead person cannot be therapeutic for them, it can still cause them serious disbenefit. For Jews this disbenefit includes added time between death and funeral, something we try to keep to a minimum. But for all of us, if the tissue was not freely given by the person or their family, we encounter questions of ownership, and from there of who may benefit from our organs. It is already the case that some freely donated organs are used in private procedures which are financially beneficial for the doctors and hospitals involved. If the organs are not a gift, should not the donor benefit?

To presume consent to this procedure is to take away our autonomy, to challenge who owns and has responsibility for one’s own body; it means that what we do now as a response to the commandment to not stand idly by the blood of our neighbour would stop being our mitzvah and become an act of the state.

This may become acceptable to an informed and consenting population, but our third criteria must be demonstrated, that the method of presumed consent would increase the number of organs for donation, and this is far from proved in every review so far.

While, currently, consent is not achieved from every potential donor, consent is not the real issue for the low rates of donation here. We have a similar consent rate to the United States, but we convert this into only half the number of transplants. We have not created and resourced an infrastructure which can take advantage of all the willing donors there already are, and presuming consent for donation will not fill that lack.

Based on a negative mitzvah of not standing idly by, pikuach nefesh has been elevated to a mitzvah that can supersede almost all others, yet not to fulfil it does not bring punishment.

On this basis, it seems clear that the Jewish community should invest in encouraging each other to register on the organ donation database, something shown to be hugely successful from campaigns such as that for Sharon Berger, but we should not endorse any idea that our consent must be anything else except freely given.