c52,
LAM - most long haul flight from the far east and many from hte middle east use LAM. This is mainly due to the great circle routes. Without wishing to appear teach you to suck eggs, a straight line drawn on a two dimensional map does not represent the shortest route; you need to use a globe. Flying from Singapore to London takes you up over Russia and approaches London from the north east.
Also, many flight from northern Europe, Germany, Belgium, The Netherlands etc arrive at LAM. Dover is one of the more busy sectors of airspace, so it doesn't make sense to force everything through to the 'nearest' holding stack; that would just cause undue delays as flow control would result in ATC slot delays. Flows around Europe are designed to be 'spread out' to allow more aircraft to fly. This is not just an LHR issue, it occurs at most major airports in Europe.