The fees are part fuel surcharge and part tax. If you fly long haul on BA departing USA you cannot avoid the fuel surcharge. However the tax that I think you probably have in mind is the UK air tax. You only pay this if your journey starts or finishes in the UK. If you are just transiting through London you will pay the lower tax relating to your final destination instead, so if you want to go to mainland Europe with a (<24hr) change of plane in London then you will not have to pay the higher taxes.