Know nothing about medical law but as a very small side line you could mention the use of consent to discredit an assault.
Examples that spring to mind are Queensbury Rules in boxing. It is OK for two 18 stone men to punch eachothers heads really hard, but if one of them kicks, then it is assault.
Also, and I forget the name of the case, there is a rather sordid S and M case where two consenting homosexual adults undertook quite barbaric acts of sexual torture on eachother, totally consensual. However, their antics were filmed and discovered. They were both taken to court for GBH with intent even though there were no reporting victims as such. I think they were nailing their testicles to wooden tables or something equally as fun.
I am sure somebody with a better memory than may may be able to quote the case.