1. Medical Ethics
UK Law on Euthanasia

2. Euthanasia and assisted suicide are illegal under English law.
Depending on the circumstances, euthanasia is regarded as either manslaughter (where someone kills another person but circumstances can partly justify their actions) or murder and is punishable by law with a maximum penalty of up to life imprisonment. 
Assisted suicide is illegal under the terms of the Suicide Act (1961) and is punishable by up to 14 years' imprisonment.
Attempting to commit suicide is not a criminal act in itself. 

3. Euthanasia and assisted suicide are illegal under Scottish law.
Depending on the circumstances, euthanasia and assisted suicide are regarded as either culpable homicide (where someone kills another person but circumstances can partly justify their actions) or murder and is punishable by law with a maximum penalty of up to life imprisonment. 
Attempting to commit suicide is not a criminal act in itself. 

4. Passive voluntary euthanasia is legal.
An adult with full mental capacity can refuse medical treatment which will result in their death.
A doctor cannot legally override their wishes.
If a doctor were to administer medical treatment to a patient who had refused it, charges of assault and battery could be brought against the doctor.

5. Passive in-voluntary euthanasia is legal.
If Doctors and family are agreed, medical treatment can be withdrawn.
Example: Tony Bland
In 1993 Tony became the first patient in English legal history to be allowed to die by the courts through the withdrawal of life-prolonging treatment including food and water.

6. Before Tony Bland
English case law on the non-treatment of patients was restricted to newborn babies.
There had been several recorded cases of disabled neonates being 'allowed to die'.

7. In summary
All forms of active euthanasia are illegal and could result in the following charges being brought against anyone who assists:
England: Murder/ Manslaughter / Charged under Suicide Act
Scotland: Murder/Culpable Homicide
However a precedent has been set for passive forms euthanasia (Tony Bland). In practice a doctor would still probably seek a court ruling before withdrawing treatment.

8. The law and the ‘double effect’
An act (such as administering morphine) by which the doctor’s primary intention is to bring about a patient’s death would be unlawful.
However, if a doctor administers morphine with the intention of relieving pain and the patient dies as a side effect then this would not result in prosecution.
Question: How can the intention of the doctor be determined?

9. Law in Scotland
On the 24th April 1996 Lord Cameron (a judge), ruled to allow PVS patient Janet Johnstone to have a feeding tube removed so that she could die in peace. Sheila McLean, Bar Association Professor of Law & Ethics in Medicine at Glasgow commented: "Coupled with the earlier statement from the Lord Advocate (Scotland most senior law officer), that, as a matter of policy, he would not prosecute doctors who remove nasogastric feeding from patients in this condition if they have obtained the authority of the Court of Session, doctors in Scotland can now be reassured that their actions will attract neither civil nor criminal liability - assuming court authorisation has been granted."