For all those worried about the essay don't be!
Mine sucked. I was nervous and my mind was preoccupied with the interview itself and the ethical scenario.
I was meant to be interviewed at 4pm (second to last one of the day), they were running late (called in at 4:40) and they looked tired. I lost all hope.
They only use the essay to differentiate between very close candidates. I'm sure if they read my essay they would have rejected me haha.
You can't really prepare for the essay.
Relax guys, worry about it when you are given it. Focus on your interview! You do well in that, they throw your essay in the bin.