Just a couple of points - my 2 cents :
"Euthanasia should be legalised in the UK, provided that it is voluntary. Voluntary euthanasia is the act of killing a person with their consent, for example by using drugs or injections." - you are defining the concept and explaining the procedure. Why?
The question is about legalizing euthanasia - so you could delve into the legalize / don't legalize argument, without explaining the basic concepts.
Explaining the basic concepts seems to be counterintuitive, since the question is assuming that you know what it is all about.
Also, use some strong stand-alone statements (that stand out) to stress some points. Like "The right to life includes the right to death".
Would also be good to include some examples that you may remember. Even you cannot remember the specifics, they can be generic examples like "In a recent case in the US ...." and "in a similar case in Australia ..."
Hope this helps.