Aerolineas' normal Buenos Aires - Barcelona round-trip flights will operate on a "triangle" basis with a stop in London on 18/19Sep15:
Buenos Aires Ezeiza (EZE) - London-Heathrow (LHR) - Barcelona (BCN) - Buenos Aires Ezeiza (EZE).
A similar routing will be followed on 25/26Sep15 but stopping in London after Barcelona:
Buenos Aires Ezeiza (EZE) - Barcelona (BCN) - London-Heathrow (LHR) - Buenos Aires Ezeiza (EZE).
A similar concept will be implemented in October towards the end of the competition adding London to the normal Rome route instead:
Buenos Aires Ezeiza (EZE) - London-Heathrow (LHR) - Rome-Fiumicino (FCO) - Buenos Aires Ezeiza (EZE) on 09/11Oct15.
Buenos Aires Ezeiza (EZE) - Rome-Fiumicino (FCO) - London-Heathrow (LHR) - Buenos Aires Ezeiza (EZE) on 17/18Oct15.
All of the flights will be operated by Aerolineas Argentinas' A340-300's.
Source:
http://airlineroute.net/2015/05/06/ar-lhr-sep15/ via Eric Trum