When you say LHR charges are shocking, this is revenue management. Only a few of the lowest fares are sometimes made available as much capacity is blocked for connecting passengers. A quarter of the seats may already be unavailable before a single London terminating seat is sold, hence unless you book early for some services, the price always seems high.
Skipness,
The operating charges that are in place at London Heathrow are much higher to the other London airports. Though it is not easily visible via the booking engines due to how airlines classify the fees, taxes and charges and wrap them up that way.
Aer Lingus for examples have taxes and charges of £53 on a flight out of LHR, while a flight ex LGW is £20.99. Both of those amounts exclude admin fees charges by Aer Lingus as standard of £7, and the airlines fare.
Willie Walsh has went on the record as saying that the point to point model is significantly challenged at LHR due to the higher operating charges that are in place and furthermore, he cites this as a reason that bmi struggled to compete and find its place on short haul, hence their move at a time to more medium haul routes...
EI-BUD