There are a number of worthwhile activites that could already be used to increase the number of donors before bringing in such legislation. Having well-trained health professionals who are able to explain the options and procedures with relatives in their own language would be a huge start. If we can't do this under the present scheme, where such intervention can save lives, then I honestly can't see any effort being made to ensure those families who don't agree with organ donation manage to register their views, and are able to articulate them in a timely fashion to the hospital authorities. The current National organ donor register isn't consulted regularly when potential donors are idientified, so how is an opt-out register going to be mananged? The Health Service is not allowed to write to individuals asking them to fill out donor cards due to Data Protection issues - again how exactly will they manage to ensure that the wishes of those who want to opt out are respected?
Of course educated literate middle classes will be able to express their desire to opt out. What about those who don't speak or read English but who are left beside a loved one, who is still breathing and who would like time to say goodbye? Given the lack of training health professionals seem to have recevied in the whole area of organ donation to date I'm not convinced that these situations are suddenly going to be well handled in future.
FWIW I am a registered organ donor, so it is not that I personally disagree with donation. But I respect the views of those who do. To say that it is worth saving lives at the expense of freedom is a strong ideological position. Presumably those of you with this view still draw a line in the sand somewhere, especially with live donation becoming more viable for some organs?