Debbie Purdy won her battle for legal guidance in the House of Lords
New guidelines over whether people would face prosecution over assisting suicide place closer scrutiny on a suspect's motivation.
Director of Public Prosecutions, Keir Starmer, said whether a person acted "wholly compassionately" and not for financial reasons was important.
But he made it clear the advice does not represent a change in the law and does not cover so-called mercy killing.
Mr Starmer had already published draft advice following a Law Lords ruling.
The guidance is not about changing the law - assisted suicide is illegal and carries a jail term of up to 14 years.
BBC legal affairs analyst Clive Coleman
Most people die under medical supervision and with palliative care.
In the relatively few cases of assisted suicide, the investigation and prosecution process may just have got more challenging.
Focusing the guidelines more intensely on whether the suspect acted from a wholly compassionate motive brings its own problems.
It will not be easy to determine motive when the main witness in the case is dead.
There could also be relatives fighting over the deceased's estate who have an interest in ascribing a false motive to the suspect.
Keir Starmer QC acknowledges evidence relating to compassion will have to be carefully scrutinised.
Financial gain will clearly be a factor which indicates a motive, though many 'compassionate' carers who assist suicide will be relatives and friends of the deceased, and therefore beneficiaries under the will.
However, more than 100 Britons with terminal or incurable illnesses have gone to the Swiss centre Dignitas to die and none of the relatives and friends involved in the cases have been prosecuted.
This is because the authorities have the power to use their discretion under the terms of the act.
The final guidelines cover England and Wales although similar ones have been set out in Northern Ireland.
They set out a range of factors to be taken into account when deciding whether or not to prosecute.
These include whether the victim had reached a "voluntary, clear, settled and informed" decision and had the mental capacity to do so.
The person helping the victim would also be expected to co-operate with the police.
Factors such as pressurising the victim, encouraging them to commit suicide or having a history of abuse against them will make a prosecution more likely, Mr Starmer said.
The advice is slightly different from the draft version issued in September.
The focus is now more on the motivation of the suspect rather than the characteristics of the victim.
But Mr Starmer said it did not mean the policy had been tightened or relaxed and prosecution was not now more or less likely.
Director of Public Prosecutions, Keir Starmer: "The law applies absolutely to everyone"
He also said no guarantees could be offered and everyone would face a police investigation.
"This policy does not change the law on assisted suicide.
"It does not open the door for euthanasia. It does not override the will of Parliament.
"What it does is to provide a clear framework for prosecutors to decide which cases should proceed to court and which should not."
Among the most obvious changes from the draft guidance was the removal of the reference to a person's terminal illness or disability.
The DPP said this was done because it was felt it could discriminate against people with these conditions and suggest they are less protected.
FACTORS AGAINST PROSECUTION
The victim had reached a voluntary, clear, settled and informed decision
The suspect was wholly motivated by compassion
The suspect had sought to dissuade the victim from taking the course of action which resulted in his or her suicide
The actions of the suspect may be characterised as reluctant encouragement or assistance in the face of a determined wish on the part of the victim
The suspect reported the victim's suicide to the police and fully assisted them in their enquiries
But Mr Starmer made clear that other factors which remain in the guidance make it clear that it would not be appropriate to help someone who does not need assistance in actually committing suicide.
Mr Starmer acted after a long running legal fight by Debbie Purdy, from Bradford, who has multiple sclerosis.
In July, Law Lords ruled she had the right to know under what circumstances her husband would be prosecuted if he helped her travel abroad to die.
She had argued that, without clarification, she would have had to travel earlier than she wanted while she was still fit enough to go alone.
Ms Purdy said: "I am still overwhelmed and delighted by this victory. Omar and I can now get on with our lives."
Lord Carlile, chairman of Care Not Killing, which has campaigned against assisted suicide and had been critical of the draft advice, said: "These revised guidelines greatly reduce the risk of undermining existing law.
"Our main concern was that the interim guidelines singled out as a group those who were disabled or ill, thereby affording them less protection than other people under the law."
FACTORS IN FAVOUR OF PROSECUTION
The victim was under 18
The victim did not have the mental capacity to reach an informed decision
The victim had not reached a voluntary, clear, settled and informed decision
The suspect was not wholly motivated by compassion, for example they stood to gain in some way
The suspect pressured the victim or had a history of abuse against them
The suspect was unknown to the victim
The suspect was paid by the victim or was working for an organisation which provides facilities for a person to commit suicide
The suspect was acting in his or her capacity as a doctor or other caring role
But he warned there were still some "flaws and problems", such as how compassion is to be assessed.
And Richard Hawkes, chief executive of Scope, the disability charity, said: "Many disabled people are frightened by the consequences of these new guidelines and with good reason.
"There is a real danger these changes will result in disabled people being pressured to end their lives."
The changes were also debated in the House of Commons with MPs expressing concern that Parliament was being bypassed.
But Prime Minister Gordon Brown welcomed the advice, pointing out the law had not been changed.
And Sarah Wootton, chief executive of the Dignity in Dying campaign, hailed the guidance as a "victory for common sense and compassion".
"The guidance represents a significant breakthrough for choice and control at the end of life for those who feel they are suffering unbearably."
But she said she would still push for a change in the law as people really needed an up-front guarantee against prosecution.
The framework comes into force immediately after a consultation which gathered nearly 5,000 responses.
It does not affect Scotland which does not have a specific law on assisted suicide.
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