Dr Peter Saunders, from Care Not Killing, a UK based organisation which promotes care and opposes euthanasia said Paul Lamb is seeking a "very radical change in the law."
He said: "If he was successful in getting that legal change it would drive a coach and horses through not the suicide act but the murder act as well and that would put a lot of vulnerable, elderly people at risk
"The proper place to be making this decision is not in court, it's in Parliament", he added.
More top news
Michael Danaher, 50, killed book dealer Adrian Greenwood at his home over a £50,000 first edition copy of Wind In The Willows.
The former Cardiff South and Penarth parliamentary candidate joins Suzanne Evans, Paul Nuttall and Raheem Kassam in the race.
From unnecessary X-rays to misguided blood tests, here is the full list of treatments health experts say will not improve your health.