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Market-wide Half Hourly Settlement (MHHS)

Market-wide Half Hourly Settlement (MHHS) is a key enabler of the flexibility to support the transition to Net Zero. The industry-led MHHS programme was created to implement the Target Operating Model (TOM) approved by Ofgem to deliver a faster, more accurate Settlement process for all market participants by introducing site-specific reconciliation using Half Hourly meter readings. The MHHS Programme will contribute to a more cost-effective electricity system, encouraging more flexible use of energy and helping consumers lower their bills.


  1. MHHS Programme
    1.1. MHHS Programme Plan
    1.2. MHHS Design
  2. The REC and MHHS
    2.1. REC Participation in the MHHS programme
    2.2. MHHS Impacts on the Retail Energy Code
  3. MHHS Code Drafting
  4. Consequential change
  5. Qualification
  6. Communications


MHHS Programme 

The MHHS Programme objective is to maximise the opportunities provided by smart metering by developing and implementing an enduring process for MHHS that delivers benefits for Consumers and enables a smart, flexible energy system.

MHHS reform will see the electricity industry working together in a significant move forward in how electricity is used and accounted for. Ofgem have placed responsibility of the MHHS Programme on the industry to deliver the programme. Elexon are the Senior Responsible Owner (SRO) and Implementation Manager (IM) of the MHHS Programme.

The MHHS Programme website provides all the information on the background, programme delivery, design and implementation for MHHS. 

The MHHS TOM can be found at the bottom of the Programme Overview page.

MHHS Programme Plan

Migration to the MHHS TOM and the date from which the new Settlement timetable will become effective are determined by the MHHS Programme Plan. Dates are subject to change by the programme and can be found on the Planning pages of the MHHS programme website.

MHHS Design

In order to implement the MHHS TOM, the MHHS Programme has created, baselined and published a set of end-to-end design artefacts. Further information can be found on the MHHS Design pages of the MHHS Programme website. 


The REC and MHHS

The Retail Energy Code (REC) and its stakeholders will play an integral role in the new MHHS arrangements. The Retail Energy Code Company (RECCo) is responsible for ensuring that MHHS requirements that impact the REC and REC Services are delivered and that the solutions have positive outcomes for Consumers. RECCo is leading the programme to deliver these activities and is working with the REC Code Manager, REC Service Providers and the MHHS Programme to ensure the required changes are successfully delivered, in accordance with the MHHS Programme Plan.  

More detail can be found on the Our Programmes page on the RECCo website. 

REC Participation in the MHHS programme

The REC has representation throughout the MHHS Programme governance structure and working groups. RECCo has a seat on the MHHS Programme Steering Group (PSG) and Level 3 governance groups, and regularly participate in working groups across design, code drafting, testing, data, migration and planning workstreams. More about MHHS Programme governance can be found here.

MHHS Impacts on the Retail Energy Code

The implementation of the MHHS TOM will see changes throughout the REC, including: 

  • Changes required to REC Category 1, 2 and 3 documents 
  • Changes required to the Energy Market Data Specification, including REC-owned Market Messages and Data Items
  • Changes required to the Electricity Enquiry Service (EES) and Central Switching Service (CSS)
  • Changes required to REC governance and Code Manager services


MHHS Code Drafting

Changes to the Retail Energy Code (REC) legal text, that are required to support MHHS implementation, are being delivered under the governance of the MHHS Programme alongside the drafting required for other industry codes. This activity is known as MHHS Code Drafting and the REC MHHS programme has dedicated expert resource leading the associated REC drafting. Code Drafting is being developed and consulted on with industry in tranches, throughout 2023 and 2024.

The Cross Code Advisory Group (CCAG) is the decision-making body, within MHHS Programme governance, that oversees the coordination, consultation and agreement of the Code Drafting. The CCAG is supported by a subgroup – the Code Drafting Working Group (CDWG). The CDWG is open to all industry stakeholders and is intended to facilitate discussion on the approach to code drafting. REC stakeholders are encouraged to attend CDWG meetings to highlight any specific queries or comments relating to MHHS code changes that require wider industry discussion.

Where issues are identified through MHHS consultations that do not relate to the MHHS arrangements, then the REC MHHS team and the REC Code Manager will work together to ensure this feedback is collated and considered under REC business as usual activity.

For further information on MHHS Code Drafting activity, including the Code Drafting plan, go to the Code Governance pages on the MHHS Programme website.

Code documents that are impacted, known as Code Artefacts, are available on the Code Artefacts pages on the MHHS Programme website. All documents are available with tracked changes. 


Consequential change to the REC

Not all the impacts to the REC, and other codes, are specified within the MHHS design. The application of the MHHS design results, however, in consequential impacts to the Code that have not been addressed by the MHHS design. These changes have been developed outside the MHHS Programme governance. Wherever possible they are agreed under REC governance in time to be fed into the overall MHHS Code Drafting. The legal text for these solutions will then be reviewed, consulted on and approved under the MHHS Programme.

Within the REC, these solutions are being governed under the MHHS Stakeholder Advisory Group (MSAG). Solutions that have been agreed can be found under the Solution Documents on the MSAG Committee Page on the REC Portal.

Where consequential changes have proven particularly complex and material such that industry consensus could not be appropriately agreed via the MSAG, these have been progressed through the standard REC change process to ensure the relevant controls in that process apply to the solution taken forward. 


MHHS related REC Change Proposals

There are a number of MHHS-related REC Change Proposals that have been progressed outside the main programme governance. These are:



Main article: MHHS Qualification

The purpose of MHHS Qualification is to confirm that Parties are ready to operate under the required industry processes and standards for the new MHHS arrangements. All REC Parties wanting to operate in the new market arrangements will need to qualify through MHHS Qualification. 


Communications and who to contact

The REC Code Manager, RECCo and the MHHS Programme are working together to ensure REC Parties and stakeholders have the best opportunity to have timely access to information about activities and decisions relating to the implementation of MHHS.

Weekly updates from the MHHS Programme can be found in their newsletter The Clock

REC MHHS activities will be communicated through the normal REC communications channels, and where appropriate will also be highlighted in The Clock.

The Code Manager will also look to highlight through REC communications channels key MHHS-related activities, from the MHHS Programme and other code bodies, that impact REC stakeholders.

The following are the key contact points in the MHHS Programme:

Contact the REC MHHS Programme team at

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