Campaigners have identified a number of cases where people who have helped others to end their lives have not been jailed and, in some cases, have not even been prosecuted.

A poll for The Times found that most people in Scotland think the authorities should turn a blind eye to such cases.

James Chalmers, regius professor of law at the University of Glasgow, said that, in light of such cases, “people are not risking as much in assisting in suicide”.

He said: “There has probably been a gradual trend towards leniency. Prison is there to protect the public, but there is no real risk of the crime being committed again so what good is a prison sentence going to do?”

Twice the Scottish Parliament has rejected bills that sought to legalise the practice.

In Ayrshire last year two spouses avoided jail after smothering their partners. In another case, Iain Kerr, a GP, admitted to helping his patients die. Helen Cowie, from Glasgow, took her paralysed son to Dignitas in Switzerland.

Police did not bring charges.

Amanda Ward, chief executive of Friends at the End as well as a legal adviser on the last bill, undertook the case history research.

She said: “There are a growing number of cases where doctors and relatives are helping dying people to end their lives. The court decisions we have seen in Scotland suggest judges sympathise with them.

“However, the circumstances can only be investigated after the death, when the victim cannot explain what was motivating the accused, and the situation results in otherwise law-abiding citizens being prosecuted.

“Changing the law on assisting a death would help prevent people taking the law into their own hands.”

Alyson Thomson, director of Dignity in Dying in Scotland, said: “The current law is unsafe and, unlike an assisted dying law, does not protect vulnerable people. We are calling for a compassionate law with up-front safeguards – rather than a criminal investigation.”

Gordon Macdonald, chief executive of Care Not Killing, which opposes legalising assisted dying, said: “When presented with all the facts and arguments, growing numbers see the very real dangers assisted suicide presents.”

A Crown Office spokesman said: “Prosecutors consider cases and assess whether a crime has been committed, whether there is sufficient evidence and whether it is in the public interest to take proceedings against the accused.

“Legal reform is a matter for the Scottish Parliament.”