Click on 'Fare Information'

Enter a city or airport in the country of interest as both the departure airport and the arrival airport
(so for example, if you're wanting the ex-UK fares you can enter LON for both departing airport and arriving airport, or LHR for both, or MAN or...)

Put the airline code of a Oneworld airline in the airline(s) field (e.g. BA)

Put 'D' in the Class Code

Choose a Currency (e.g. GBP)

Click 'Search'