I can't quite make the tax add up to the same amount but here is the breakdown:
40.00GB = UK APD
7.90UB = UK Passenger Service Fee
1.30AY = US Passenger Civil Aviation Security Service Fee
14.80US = US Transportation tax
2.50XA = US Animal and plant health inspection services user fee
2.20XF = US PFC
3.50XY = US User immigration fee
2.70YC = US Custom user fee
You have to go through all those US services and they charge you for them.