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Market-wide Half Hourly Settlement (MHHS) Milestone 8 (M8) is the date in the MHHS implementation plan for ‘Code changes delivered’.
The Retail Energy Code (REC), along with other Code Bodies, is therefore planning a release for the date in the plan associated with M8. This has been approved for September 2025.
The primary REC Change Proposal that provides the changes required to the REC legal text to support MHHS implementation is R0209 - Implementation of MHHS Arrangements. Additional drafting amendments have also been made under R0241 - MHHS Incremental Changes for go live.
The drafting has been developed under the Programme’s MHHS Code workstream and was approved by Ofgem, via R0209, on 26 November 2024. Further information on the development of the code changes can be found on the MHHS Code Drafting Wiki page. R0241 was developed through a REC Change Issue and was reviewed and endorsed under the Code workstream prior to consultation.
REC Schedules and documents approved under R0209 and R0241
The REC Schedules and documents approved under R0209 and R0241 are provided below:
- Schedule 1 – Interpretations and Definitions MHHSv1.2, updated version approved under R0241
- Schedule 9 – Qualification and Maintenance MHHSV1.1, updated version approved under R0241
- Schedule 12 – Data Access MHHSv1.0
- Schedule 14 – Metering Operations MHHSv1.2
- Schedule 15 – Metering Accreditation MHHSv1.0
- Schedule 19 – Market Exit and Supplier of Last Resort MHHSv1.0
- Schedule 23 – Registration Services MHSSv1.1
- Schedule 24 – Switching Data Management MHHSv1.0
- Schedule 27 – RMP Lifecycle MHHSv1.0
- Schedule 28 – Related Metering Points MHHSv1.2, updated version approved under R0241
- Schedule 29 – Address Management MHHSv1.0
- Schedule 30 – Resolution of Consumer Facing Switching and Billing Issues MHHSv1.1
- New Schedule XX – MHHS Migration MHHSv1.4, updated version approved under R0241
- Consolidated Metering Code of Practice MHHSv1.0
- EES Service Definition MHHSv1.2, updated version approved under R0241
- EES API Interface Specification MHHSv1.1, updated version approved under R0241
- ERDS Service Definition MHHSv1.2, updated version approved under R0241
- EMDS Standards Definition Document MHHSv1.0
Data Specification approved under R0209 and R0241
Changes to REC-owned elements of the Energy Market Data Specification (EMDS) were also approved under R0209 and R0241. The REC specific DTN changes can be found in the following documents:
- Consequential Change Solution - REC-Owned Market Messages - Contains a summary of the DTN updates included in R0209
- REC-owned DTN updates R0241.zip - updates to D0300, D0383, D0384, J2240
All the REC-owned data specification updates can be found alongside Market Message and Data Item changes and additions for all the industry codes:
The pre-release versions of EMDS and the Data Transfer Catalogue were published on 8 September 2025, on the Data Specification Pre-Release Information page on the REC Portal.
Previously, EMDS HTML vMHHS 1.2 was published on 28 February 2025 and corrected errors identified in version 1.1, approved under R0209. It was also updated to reflect MHHS Design Interim Releases 8.2 to 8.8
- Energy Market Data Specification HTML vMHHS 1.2, including all Market Message and Data Item changes
- The changes included in EMDS vMHHS 1.2 are documented in M8 Change Control Log
- Please also see the EMDS vMHHS 1.2 Guidance Notes
- This was a working draft and parties have been directed to continue to use the MHHS Design Artefacts for their MHHS design, build and testing.
Further information
Will there be any further changes to the REC?
It was recognised that there would be some incremental changes to the MHHS code drafting following changes identified during the Programme’s systems integration testing (SIT) and since R0209 was submitted for approval. R0241 - MHHS Incremental Changes for go live was raised to progress and deliver these changes. The EMDS changes detailed above were taken through the REC change process under this change.
Will there be any other changes implemented in the MHHS M8 release?
A number of other changes have also been tied to M8 due to their dependency on MHHS implementation:
- R0044 - MHHS Programme Changes required to Central Switching Service and R0097 - Consequential Change for CSS Smart Meter Data Retriever Appointments
- R0083 - Changes to Supply Number Format for MHHS
- R0222 - ESME ID Update Rejections
- R0264 - Data Specification Housekeeping
The full list of changes for all REC releases can be found on the REC Releases page on the REC Portal.
Some Category 3 changes will also be included in the MHHS M8 release. Details on updated and new Category 3 documents, and when they are being implemented, can be found in the MHHS Category 3 Document Updates Wiki article.
How will the MHHS M8 release be delivered?
The Code Manager has developed a plan in collaboration with RECCo, which ensures the preparation of the MHHS code drafting in EMDS and the Digital Navigator is completed in time for the REC release for MHHS M8.
The majority of the changes will be made through applying the approved redlined changes to the existing code. However, Schedule 14 – Metering Operations and the new Migration Schedule will be implemented as whole new documents as explained under R0209.
When the MHHS Code Drafting is implemented at M8, the REC version will be uplifted to REC V4.0.
The Code Manager hosted a MHHS M8 2025 REC Release Webinar on 16 July 2025 which provided an overview of the Change Proposals included in the M8 REC Release due to be implemented on 22 September 2025.
Take a look at the REC Portal Event Page for the recording and slides from the webinar.
How are the system changes being managed?
The systems go-live is being managed under the MHHS Programme, under the associated MHHS Milestone M10. The targeted systems go-live date is the same as M8, 22 September 2025.
The changes to the Electricity Enquiry Service are part of the M10 cutover. Information specifically on the EES cutover and impacts to users, can be found on the dedicated Blog Post on the REC Portal.
How will amendments to Schedule 14 from other Change Proposals be maintained?
Changes to Schedule 14 have only been progressed under other change proposals where they do not impact the MHHS Code Drafting. Alignment of such amendments will be managed during the release preparation activities.
Will there be an updated version of the MPRS Validation Rules document to support REC Parties in addition to the REC documentation?
Yes, the Meter Point Administration Service provider has shared MPRS Validation Rules v9.0.0.2, which includes the amendments to reflect the MHHS arrangements. This document should be read in conjunction with the new Balancing and Settlement Code (BSC) Procedure, BSCP706 ‘Supplier Meter Registration Service for MHHS Metering Systems’ which defines the Supplier Meter Registration Service (SMRS) validation rules.
The live version of the document on the REC Portal will be replaced as part of the M8 release activities.