Historical series of electricity and gas fixed tariff indices

FOI reference: FOI-2025-2853

You asked

Following the recent transformation of the inclusion of fixed price energy tariffs in consumer inflation, there is an impact chart in this 'Notification of proposed changes' letter from the ONS. Could you please provide the historical series of electricity and gas fixed tariff indices that were used to construct the chart?

We said

Thank you for your request for the historical electricity and gas fixed tariff indices that were used to assess the impact of fixed tariffs on the Retail Prices Index (RPI).  

Please see the associated spreadsheet, named FOI 2025 2853, in response to your request. This contains unchained indices referenced on the previous January = 100, which were used to produce the constructed all-items RPI in figure 1, and continuous, chained indices referenced on January 2019 = 100.  

The series have been constructed using available historical data but please note that there are caveats to the analysis. These include the low number of fixed tariff data points available in 2022 to 2023, when the difference between the constructed and published RPI 12-month rate was at its greatest, and the fact that we have not had the resources to quality assure the historical series to the same degree as if they were used in live production.