He is not a typical campaigner. But behind his quiet manner is such a firm belief that assisted suicide should be legalised in Scotland that he has taken the extraordinary step of describing how as a GP he helped patients who wanted to end their lives.
He did not embark on his medical career to do this. Instead, he said, he formed his views through reading and experience with patients over the years.
Surprisingly he said Dame Cicely Saunders, credited with founding the hospice movement, made an impression on him early on. Dr Kerr, an atheist, is a volunteer driver for a hospice today.
He said: "Cicely Saunders noticed doctors and nurses actually spent much less time with people with a terminal diagnosis and these people became more isolated as their needs increased. I think I was for a long time aware of the appropriateness of doctors discussing end-of-life issues or at least giving patients an opportunity to raise the subject."
When a husband and wife who were patients at his Clarkston, East Renfrewshire, surgery asked him in 1990 for help with a joint suicide, he did not think the request unreasonable.
Dr Kerr said: "He had circulatory problems. He had difficulty walking. His eyesight was failing. He could not get out as much as he wanted to. He could not see the television properly. He was in his 80s. He just felt it was an appropriate thing to do.
"His wife was actually not ill but she was a bit agoraphobic and would not go out without him. I think a lot of people would not think that was really necessarily appropriate for assisted suicide.
"But they had medical conditions which they felt impaired the quality of life to such an extent they felt they did not want to go on together." He said after ensuring they had told their daughter their wishes, he provided the sleeping tablet sodium amytal for the couple.
"I went and got the stuff for them. I did not want their daughter to get into any difficulty or problem with it," he said.
The deaths of the couple, side by side, and the involvement of their GP was reported by The Herald at the time. The article quoted a neighbour who, when told the mode of their deaths, said: "I think that is wonderful. If that is what they decided to do, to die peacefully together, then I applaud their courage."
When another patient wanted information about how to kill himself with a now old-fashioned antidepressant, Dr Kerr sought guidance from a colleague. On his advice, Dr Kerr said he not only gave the patient the information but visited him while he was dying over several days.
The GP said it was not distressing. "I was just concerned that I had not given him proper advice," he said. "I was not concerned for him because that was what he wanted, he had said on numerous occasions."
In his 35-year GP career, Dr Kerr recalls two other patients requesting help to end their lives. One is the woman known from the GMC hearing into the case as Patient A. Dr Kerr gave her a prescription for sodium amytal but she later died after taking a different drug. He promised to help another seriously ill patient if she felt it necessary, but she died from natural causes.
Dr Kerr has never been worried about being prosecuted for his actions. He said: "I feel that the law is out of step with what is socially acceptable to a large number of people. People do not have the option to be assisted to end their life rather than to continue with symptoms - they consider to be intolerable."
Now retired, Dr Kerr, 66, is keen to talk to audiences about assisted suicide, such as Rotary Clubs, in a bid to involve ordinary people in the debate. This, he said, is so they can inform MSPs of their views to represent them when MSP Margo MacDonald re-introduces a bill on assisted suicide to the Scottish Parliament this year.
"The worst thing about death is not being alive," he said. "If being alive is not a bunch of cherries, what is wrong with embracing death?"