It's so rare that something sounds too good to be true and is neverthless true.
From February 2018 the Norwegian budget airline is starting scheduled non-stop flights by Dreamliner from London to Buenos Aires. It will take about 13 hours, which is amazing. Even more amazing - outside peak holiday times the cost is under £600... Just be aware it'll cost another £25 to put a bag in the hold, and you still won't get anything to eat, but it's still much faster and cheaper than anything else that flies.
Booking is already open.