Deleted - see Airbubba post below. (Got it now Airbubba, tape link wasn't working for me earlier).
From the time the decision to abort the flight and land was taken, until the wheels actually touched down, was probably little different between returning to LHR or circling to dump fuel and land at Shannon. A return to LHR would be the obvious choice if the emergency is considered insufficient for an immediate landing at the nearest suitable/available airport.
Last edited by parabellum; 16th Feb 2016 at 04:26.