In a case in 1993 (2-), Tony Bland who went into a persistent vegetative state following the Hillsborough disaster had his feeding tube withdrawn, but this was not considered murdered as it no longer promoted his best interests (had he requested that the tube not be removed, then removing it would have been murder).
In Holland, euthanasia was decriminalised in 1993 and formalised in 2002. Doctors must have an explicit, long-standing, informed and voluntary request from the patient and it must be a last resort. A second doctor must be consulted and the case must be reported. About 2.5% all deaths in Holland are due to euthanasia with only 54% being reported and 1000 having made no explicit requests and 250 being involuntary. Apparently in Holland, old people are worried about going to hospital because they fear being euthanised!
In Belgium, euthanasia was legalised in 2002 with a euthanasia committee supposed to examine every case. It represents 2% of all deaths in the country, but a study found that 66/208 cases had not been preceded by a request. This is obviously bad.
In Switzerland, assisted suicide is legal as long as it is for altruistic motives. You probably know about Dignitas, the famous euthanasia clinic in Switzerland.
The Oregon Death With Dignity Act states that in Oregon, Washington State, Montana and Vermont in the USA, if a patient makes a written request 15 days apart then they may be given lethal medications.
How to answer a question about euthanasia
This is a very interesting situation because all four principles come into play and they seem to be at odds with each other. Justice and non-maleficence standing on one side with it being wrong to kill another human and beneficence and autonomy on the other suggesting it is better to end their suffering and allow them to die with dignity on their own terms. There are clear arguments both ways, but the danger of the slippery slope of “will people who feel like a burden feel forced to opt for euthanasia?” and the shoddy record keeping of those countries where it has been legalised seems to solidify the case for most countries to stay opposing the practice.
1- R (Pretty) v DPP  and Pretty v UK 
2- Airedale National Health Service v Bland