The Department for Transport does not hold this information. The Office of Rail Regulation publishes "National Rail Trends" on a quarterly basis, available at:
This document contains a variety of industry information and statistics including a national fares index.
Negotiations between the train operators and Transport for London to enable the use of Oyster pay-as-you-go as a payment method for National Rail fares across the London Travelcard area are continuing. There is no association between Oyster pay-as-you-go introduction and fares regulation.