The Future of AM Radio (regularly updated article on the Frequency Finder website) Page 4

The BBC announced on 15 April that Radio 4 long wave will close by the end of 2026 with at least two months’ notice of the exact date.
For the past few years, an increasing proportion of the BBC’s long wave transmission costs (but not those of the Radio 4 MW transmitters) have been funded by the electricity industry. This uses phase information in the long wave transmissions to provide the Radio Teleswitch Service (RTS) which switches ‘Economy 7’ electricity meters between day and night modes. This was originally due to end in 2020. However, due to delays in smart meter installation, the contract has been extended several times. The plan is now to phase out the RTS gradually from 30 June 2025 onwards,
noting that different messages are sent to different groups of meters. 30 December 2025 had been reported as the latest date the transmitters can be maintained until. However, Droitwich was switched to reduced power in spring 2025, which should enable it to last longer. It has been estimated that replacing all RTS meters will take about a year at the current rate of progress, suggesting a summer 2026 final closure of the RTS. Rumours circulated in August 2025 that BBC transmissions on long wave will end of 26 September 2026 – this is likely to be the earliest date that the long wave service may close on.
The BBC stopped scheduling separate content on Radio 4 Long Wave at the end of March 2024 (having announced this on 29 May 2023). Radio 4’s medium wave transmitters then closed at the end of April 2024, (with retune messages from 15 April).
http://www.frequencyfinder.org.uk/Opinion_AM.pdf

The BBC announced it would close longwave at some point in 2012, discussions with the electricity industry in 2014 led to the agreement that the electricity industry would pay a high proportion of the costs IIRC in 2017 until 2020, agreement extended with electricity industry then paying the vast majority of the costs.

Elexon 12/01/2023
The contract between Elexon and the Energy Networks Association (ENA) to pass the operational costs for the Radio Teleswitch Service (RTS) through the BSC as ‘BSC Costs’ is due to expire on 31 March 2023. The BSC pass-through operational costs are expected to rise from c.£1.5m to c.£5m

Summary
The BBC have advised the ENA that the operational costs for the RTS are rising primarily due to increases in the cost of electricity needed to power the Long Wave Radio transmitters (as advised by the BBC). It’s worth noting that due to its strict internal financial governance controls, the BBC are not permitted to make a profit on, nor subside any of the costs of providing the RTS service.

https://www.elexon.co.uk/bsc/smg-issue/issue-104/