Looks like they've noticed their little boo-boo
ECONOMY class fare to EZE ex-LHR now back to a respectable 531 pounds total, whilst Business Class sells at over 2,000...so slightly more expensive than 320 pounds.
For those still interested in flying down there for a cheap price, opodo are offering flights on Swiss (Y) for 465 total; unijet.com have a fare of about 474 total with Air France......pretty good deals, really.