It looks like it was added into the ticket. For tickets on or before Oct 31, the APD is £90, and after that it is increased to £120. The taxes you paid should have looked something like this:

USDA APHIS Fee $5.00
US Immigration Fee $7.00
US Customs Fee $5.50
US International Arrival Tax $16.10
United Kingdom Air Passengers Duty £90.00
United Kingdom Passenger Service Charge £22.97

With this, taxes amount to ~US$204, so what you paid seems correct.