You misunderstand entirely. I'm not comparing what Shipman did to what a designated relative might do under such regulation in any sense at all. The point is if we had the 'assisted suicide' rules, and
if the doctor could also be the witness to the 'statement of intent to relinquish life' as we may call it would likely have been very, very hard to convict Shipman of anything at all. He could have got his victims to mistakenly sign the statement before he killed them. He could have killed them and faked the statement afterwards - he faked prescriptions to get the drugs he injected his victims with. Most of the people he killed were old and frail and thus a lax system of checking would likely not bother examining the circumstances too stringently. However if someone else had to be the declaration witness each time, he wouldn't be able to hide behind the 'assisted suicide' regulations.
I'm not saying the people who might help relatives in this regard are serial killers. I'm saying if you have a system, you have to have it work in such a way as it can't be abused by someone like Shipman. If one person handles the whole process, it's open to abuse.
Jon