Bear in mind that £85+ of the £129 is tax and airport charges. You have £40 APD plus the other Gatwick departure charges; and most of the American taxes are charged on arrival (and there are an awful lot of them).

By comparing Oasis’ £75 one-way to HKG with Zoom’s £129 to JFK, you are not comparing apples with apples. Oasis’ £75 fare is before taxes and the actual price you pay for a one-way LGW-HKG is £152.30. Zoom’s £129 fare LGW-JFK includes taxes and the price you pay is £129.

It’s also not easy to get anything below £450 return on the big airlines between LON and NYC during July and August.