From my experience around 30 years ago with an elderly relative I would argue that we already have euthanasia in this country however it's just not officially recognised / sanctioned / openly admitted
Without going into detail from what I saw the medical staff appear to assess an old person considering age and condition then make a judgement as to whether they think they will survive or how long and what the cost will be then decide whether to give medical treatment.
So for instance someone with a particular condition age 60 may get good treatment whereas the next person age 90 may not, my understanding is once they start giving treatment they struggle to withdraw it but if they never start treatment they can effectively kill someone, perhaps times have changed but it all comes down to cash
Anyway back to the question and yes I do agree with "Assisted dying" so long as the correct safeguards are in place to stop it becoming a way to bump off Grandma to get the inheritance etc
I've not seen it 1st hand but I know people who watched their parents dying from cancer in an exceptionally painful way, one friend was there at the point his Mum died while coughing up blood, it stays with you forever.
I have thought about this subject quite a lot and I guess everyone's stance is a bit different depending on their circumstances and whether they have a partner / kids / grandkids etc
The best option is obviously to die peacefully in the night following a particularly intense punt the day before and a couple drinks of your favourite tipple just before bedtime but we don't normally get to choose like that, unfortunately
Personally if I get ill and decline to the point where I don't feel that I have a good Quality of life then I intend to go at the time of my own choosing
Unfortunately as already said we don't always get to choose but I hate to think that I will end up sat in a chair in a care home for years on end doped up to the eyeballs and sitting in a piss stained chair until the money runs out that is