Offence that is punishable by up to 14 years in prison

It is illegal under the Suicide Act of 1961, which says that a person who "aids, abets, counsels or procures" the suicide or attempted suicide of another person commits an offence.

The Criminal Attempts Act of 1981 can also be used to bring prosecutions, as it makes any attempt to help someone commit suicide illegal - even if the help is given in countries where it is legal, such as Switzerland, Belgium and the Netherlands.

The CPS can inquire into the circumstances of assisted suicides after the event - there is no time limit for people to escape being taken to court. But prosecutors have considered eight cases of assisted suicide abroad and none has resulted in prosecutions because of insufficient evidence.

The parents of 23-year-old rugby player Daniel James were not prosecuted after his death in Swiss suicide clinic Dignitas in September last year. A rugby accident had left him paralysed from the chest down.

The decision was made by Keir Starmer, the Director of Public Prosecutions, and was seen by some as a "green light" for people to take relatives abroad to commit suicide.

The detailed ruling said Daniel's parents had helped him send documentation to Dignitas and to travel there, which could be seen as "aiding and abetting". But they were not "ringleaders" or "organisers" of the suicide, and had tried to dissuade their son from his decision.

Mr Starmer later rebutted the suggestion he was opening the way to assisted suicide.

Multiple sclerosis sufferer Debbie Purdy is attempting to clarify the law.

She wants a guarantee that her husband would not be prosecuted for taking her abroad for an assisted death.

But there has been no definitive ruling from the High Court or the Court of Appeal and it is now being considered by the Law Lords.

Lord Joffe has proposed an amendment that would see "mercy killers" facing manslaughter charges rather than murder charges.