Una Due Tfc, I will turn it around a bit - the main reason for British Airways being one of the European airlines with the poorest on time performance is LHR. KLM had the best on time record in 2014 and their home airport is AMS. The airlines need the best tools, and the 2015 edition of LHR is definitely not the best tool - it's overloaded big time.
For me the big fright is an incident over London city centre that don't manage to crawl over the perimetre fence as flight 38. With such a high utilization as today the margins are cut to the bare minimums, and balancing on such a tightrope can be fatal. Not the best for what will be seen as a premium airport and a world class hub.