Luiz Horta of Brazil and Reid V Rappaport of Florida both helpfully pointed out that much the easiest route to Mendoza is to fly to Santiago and Chile and then, from the same airport (cf Buenos Aires) take the stunning flight over the Andes to Mendoza. (You hardly seem to get higher than Aconcagua.)
They are right of course but it's not so easy to get to Santiago from London, especially not with British Airways. I must say that BA's Ch de Cruzeau 2005 Pessac Leognan Blanc was tasting particularly well on my prolonged flight out... (See my recent tasting...