Originally Posted by NickB

There is nothing strategic about this and more to do with historic, political and economic ties.
The only airline for which that argument might have some validity is AY, which has deliberately tried to project HEL as a Asia-Europe gateway (but even then, the range of destinations they serve in Asia is small compared the major European carriers).
For BA, the few extra minutes flying time involved in flying from LHR to North America compared to AMS or CDG is neither here nor there and typically swallowed by the time spent waiting in a stack in somewhere in the LON area.
As to IB, its positioning as a gateway for South America has little to do with its geographic positioning and plenty to do with the historic, cultural, economic and linguistic ties between Spain and Latin America