British Airways adds carrier-imposed surcharges on long-haul flights, sometimes $300 to $500 per leg, and those are baked into your fare if your routing uses BA metal through Heathrow. Routing via Frankfurt on Lufthansa or Helsinki on Finnair can cut that cost significantly.
Usually it is not London itself, it is the carrier. British Airways adds substantial carrier-imposed surcharges on long-haul flights, sometimes $300 to $500 per leg. If your routing runs through Heathrow on BA metal, that cost is baked into the fare you are quoted.
Heathrow is still the primary transatlantic hub in both directions and often the right answer. But it is not the only one. Routing through Frankfurt on Lufthansa (Star Alliance) or Helsinki on Finnair (oneworld) can reduce the surcharge component significantly on the same journey.
This is the kind of trade-off worth asking about directly. Your consultant will flag where the surcharge is coming from and what the alternative routing costs in time.