What is the halachic law concerning organ donation?

Dear Rabbi
I often enjoy reading your answers and thought it time I ask one of my own. In the news today was a story about an initiative to automatically put everybody in the UK on an organ donor scheme, unless they opt out. What is the halachic law concerning organ donation?
Dear Perry,
The human body is and always remains sacred even after death. That’s why there is the notion of achevra kadisha or sacred brotherhood/sisterhood that ensure the most befitting, respectful and spiritually imbued burial for the deceased. Part of that responsibility includes the idea of keeping the body intact. So much so that were one to G-d forbid has a limb amputated, that limb is immediately buried, and is later reburied with the individual upon passing. That said there are circumstances that would allow for the transfer of an organ it will go immediately to save another’s life (as opposed to sitting in a bank waiting with the risk of eventual disposal). But even here there are more and less humane ways to remove organs (say an eyeball for example) and all that needs to be taken into consideration as well. The Chief Medical Officer’s proposals are seriously problematic for the Jewish and other Ethnic communities and the London Beth Din have issued their own ruling in this regard.