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v2.1Current version

Published17/02/2026Effective date17/02/2026Release date17/02/2026

Sub-Market definitions

Document Summary

What?The rule set key elements of how a Sub-Market is designed. These are supplemented by definitions from other rules, to catalogue the different Sub-Markets. How?Core parameters are used to define each Sub-Market.Who?This rule impacts all System Operators. The clearer definitions should benefit all Flexibility Service Providers.When?This rule comes into force in February 2026Why?This rule aims to aid understanding of how individual Sub-Markets work, as well as how aligned/different they are.

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Sub-Market definitions - Flexibility Market Rules - Elexon

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0.0

Sections 1, 2, 3 and 4 form the legally binding Flexibility Market Rule.

Defined terms capitalised in this document shall have the meaning given in Section 4.

GuidanceSummary of Sub-Market definitions Flexibility Market Rule

This section is provided as guidance to the Flexibility Market Rule. Therefore, it is not legally binding and falls outside of the formal change management process.

Context

This rule establishes a common framework for defining and cataloguing individual Sub-Markets within the wider flexibility market. It translates the Open Networks “Products technical requirements document” into a set of standardised Sub-Market definitions, supplemented by parameters from related rules.

The aim is to provide clarity on how Sub-Markets are designed and to enable simple presentation and consistent comparison and alignment across the different Sub-Markets in our Flexibility Market Catalogue. The rule applies to all Sub-Markets within the Market Facilitator’s scope and comes into force in February 2026.

Sub-Market Definition Requirements

The rule sets out a number of parameters that define a Sub-Market. This includes elements such as the buyer, payment structure, procurement method, pre-qualification criteria, metering requirements, platforms, availability, utilisation, settlement, and baselining. System operators are obligated to provide the Market Facilitator with these parameters for each of their Sub-Markets, to be shared with industry via the Flexibility Market Catalogue.

We believe the impact of these requirements to be:

Impact on System Operators	Impact on FSPs
System Operators must maintain these parameters for each of their Sub-Markets.	FSPs will be able to better understand the different markets via the Flexibility Market Catalogue.

Implementation monitoring requirements

The key requirements are laid out below. A view across the rules is available in our deadline tracker.

Category

Requirement

Trigger for data submission

What we will do with it

Implementation tracking

Basic tracking of implementation status and target date

From 14/01/2026 (20 working days after the published date).

Within 10 days of change

Track whether implementation is on track via our Implementation tracker

Flexibility Market Catalogue data

Confirmation of Sub-Market parameter alignment and updates

From 06/02/2026.

Within 10 days of change

Provide an overview of Sub-Markets via the Flexibility Market Catalogue.

Effectiveness monitoring data

N/A

Derogations against this rule

The following derogations are in place:

Who	What	For how long	Why
SSEN	The full requirements for LMA Interim Payment Service	Until 01/02/2027	To prevent blockers to LMA Interim Service settlement

1Applicability of this Flexibility Market Rule

1.0

This Flexibility Market Rule applies to all System Operator Sub-Markets within the Market Facilitator’s scope. Innovation trials are not bound by this Flexibility Market Rule.

All System Operators shall provide the data set out in section 3 no later than the timings also set out in section 3.

Variations to this rule are only permitted with an approved Derogation from the Market Facilitator.

The core dates for this Flexibility Market Rule are laid out below.

Table 1: Flexibility Market Rule dates

Published Date	04/02/2026
Implementation Date	06/02/2026
End Date	-

2Sub-Market Definitions

2.1Sub-Market definition parameters

The parameters that define a Sub-market are:

Table 2: Sub-market definition parameters

Purpose	Parameter Name	Description	Required values for DNO Sub-Markets	Required values for NESO Sub-Markets
User	Buyer	Who is the buyer of the services	-	NESO
Strategic Direction	Strategic Direction	The high-level plan for the service in the near future.	-	-
Structure	Payment Structure	How the service is structured (i.e. what is the SO asking of the FSP)	As set out in the Product definitions rule (FMR-PD)	-
Structure	Procurement Method	The type of mechanism used to procure the service	-	-
Structure	When Prices are Set	Time before use that prices are determined	As set out in the Product definitions rule (FMR-PD)	-
Structure	Generation/demand turn down service or generation/demand turn up service?	Does the service require the provider to export or import power to the grid	-	-
Pre-qualification	Required to be a Balancing and Settlement Code (BSC) Party?	The rules and governance arrangements for electricity Balancing and Settlement in Great Britain.	No	-
Pre-qualification	Non-BM Party Accessible?	Can you participate without being a Balancing Mechanism Party?	-	-
Pre-qualification	Asset Location Grouping Requirement?	Requirement for where multiple assets within a unit must be located	per specific CMZ	-
Pre-qualification	Aggregation /Virtual Lead Party (VLP) Route Available?	The option of having more than a single asset within a unit	Yes	-
Pre-qualification	Minimum MW Delivery Required (also referred to as Minimum Aggregated Unit Size)	The minimum MW capacity that a unit must exceed to enter the service	As set out in the Product definitions rule (FMR-PD) under "Minimum Aggregate Unit Size"	-
Pre-qualification	Unit volume cap	Maximum amount of MW volume per unit registered in the service	-	-
Pre-qualification	Open to Flexible Connections or similar?	If the asset's network connection has 'restrictions' (eg a Curtailable, Flexible or Ramped connection), can they participate?	-	-
Pre-qualification	Open to Planned Connections?	Identifying when assets must be connected to the network before participating in flexibility market.	-	-
Metering	Asset metering permitted? (vs boundary point metering system)	What type of metering is permitted? Some services only allow boundary meter data whilst others allow metering behind the boundary i.e. asset metering	-	-
Metering	Operational Metering Required?	A live feed to the relevant System Operator control room to measure providers live service delivery	-	-
Metering	Operational Meter Accuracy Required?	The accuracy rating required of physical meters providing operational metering	-	-
Metering	Operational Meter Refresh Frequency	The frequency that the physical meter captures real-time data snapshots	-	-
Metering	Operational Metering Latency	Operational metering data must reach relevant System Operator Control Room within this time	-	-
Metering	Operational Metering Signal Type	The type of electrical data collected for operational metering	-	-
Metering	Performance Meter Refresh Frequency	The frequency that the physical meter captures real-time data snapshots (e.g. 20Hz= 20 snapshots per second)	-	-
Platforms	Service Registration Platform	The platform used to register to enter the service	-	-
Platforms	Procurement Platform	The platform that providers use to bid into the service and form contracts	-	-
Platforms	Operational Platform	The platform for operational instructions (e.g. utilisation declarations or dispatch)
Platforms	Settlement Registration Platform	The platform to register and submit settlement data	-	-
Availability	Availability period	the periods in which the service is made available or utilisation is committed	As set out in the Product definitions rule (FMR-PD)	-
Availability	Availability Payment Unit	The units used for Availability Payments	As set out in the Product definitions rule (FMR-PD)	-
Utilisation	Instruction Notice Period (also referred to as Utilisation Instruction Timings)	Notice given to providers that they will need to respond to an instruction in the immediate future	As set out in the Product definitions rule (FMR-PD)"	-
Utilisation	Gate closure	Dispatched before or after gate closure	-	-
Utilisation	Delivery Duration (also referred to as Minimum Utilisation Time)	Minimum amount of time that a provider must be able to provide its obligated delivery volume	As set out in the Product definitions rule (FMR-PD)	-
Utilisation	Utilisation period	The periods in which the service is made available or utilisation is committed	As set out in the Product definitions rule (FMR-PD)	-
Utilisation	Time to respond to instruction	Time to show unit ramping has began	N/A	-
Utilisation	Max time to full delivery from Instruction (also referred to as Maximum Response Time)	Time taken from utilisation instruction or triggering event to reach procured volume delivery	As set out in the Product definitions rule (FMR-PD)	-
Utilisation	Ramping requirements	The specific requirements of the service in relation to ramping up or down of delivery	N/A	-
Utilisation	Maximum Recovery Period	The time between the end of the delivery of one instruction and the start of the delivery of the next instruction	-	-
Utilisation	Instruction Trigger	What triggers a request to deliver the contracted volume	Tender result will be seen as instruction OR DNO instruction	-
Utilisation	Auction contract length	How long the providers delivery contract lasts	-	-
Utilisation	Utilisation Payment Unit	The units used for Utilisation payments	As set out in the Product definitions rule (FMR-PD)	-
Settlement & Performance Monitoring	Settlement or Performance Monitoring required?	Identification of any service specific performance monitoring requirements.	Yes	-
Baselining	Baselining	Summary of the baselining approach used	As set out in the DNO Baselining rule (FMR-SBM)	-
Reporting	EBR Article 18	Is the sub-market within scope of Electricity Balancing Regulations Article 18?	-	-

Null values (-) indicate that there is no required value for this parameter.

3Market Information

3.1Implementation tracking

The System Operators must provide the Market Facilitator with the data set out in Table 3 for each Sub-Market in scope of this rule. The data provided should accurately reflect their implementation of the rule within each of each Sub-Market.

The expected values required for compliance are also set out in Table 3.

Initial data shall be sent no later than 20 working days after the Published Date of this Flexibility Market Rule.

Updates shall be sent as soon as reasonably practical, and no later than 10 working days after any changes to the values.

Elexon reserves the right to publish this data within its Implementation Tracker.

Table 3: Implementation tracking requirements

FMR-SMD	Parameter	Required value (per Sub-Market)
Implementation Status	Dependent on date: Before Implementation Date: Not yet started, Implementing, Paused, Implemented Between Implementation Date and End Date: Implemented After End Date: Superseded
Target Implementation Date	No later than Implementation Date

FMR-SMD

Parameter

Required value (per Sub-Market)

Implementation Status

Dependent on date:

Before Implementation Date: Not yet started, Implementing, Paused, Implemented
Between Implementation Date and End Date: Implemented
After End Date: Superseded

Target Implementation Date

No later than Implementation Date

3.2Flexibility Market Catalogue data

The System Operators must update the Market Facilitator with the data set out in Table 4 below for each Sub-Market in scope of this Flexibility Market Rule. This should accurately reflect their implementation of each Sub-Market.

The expected values required for compliance are also set out in Table 4.

Initial data shall be sent no later than the Implementation Date of this Flexibility Market Rule.

Updates shall be sent as soon as reasonably practical, and no later than 10 working days after any changes to the values.

System Operators shall also publish this information themselves.

Elexon reserves the right to publish this data within its Flexibility Market Catalogue.

Table 4: Sub-Market definitions

Parameter	Description	Required values
All the parameters set out in Table 2

3.3Effectiveness monitoring

There are no market facilitator metrics for this rule

4Glossary

4.0

The following definitions are specific to this Flexibility Market Rule. These are supplemented by the definitions in the Market Facilitator Glossary. If there is an inconsistency between definitions, the definition in this document shall prevail.

Term	Meaning
None used in this document

FMR: Sub-market Definitions - Amendment record

Guidance

This section is provided as guidance to the Flexibility Market Rule. Therefore, it is not legally binding and falls outside of the formal change management process.

Version	Published Date	Document Status	Description of Changes	Change Proposal Reference	Market Facilitator Decision Report Ref
1.0	12/12/2025	Final	Document Published
2.0	04/02/2026	Final	Housekeeping change	CP002	CP002
2.1	17/02/2026	Final	Derogation Rule added

4.0.2

Annex 1: Associated meta-data

Guidance

This annex is provided as guidance to the Flexibility Market Rule. Therefore, it is not legally binding and falls outside of the formal change management process.

Identifier	FMR-SMD
Title	Sub-Market definitions
Type	Flexibility Market Rule
Collection	Sub-Market Alignment
Audience	NESO, DNOs, FSPs
Expertise	Market Design
Owner	Market Facilitator
Expected benefit	Deliver a common approach to defining Sub-Markets to: - aid understanding of the individual Sub-Markets and the market as a whole, - aid comparison across Sub-Markets
Related end-to-end process reference	E.1 Define Sub-market
References	FMR-PD, FMR-SBM
IsReferencedBy	FMR-PD, FMR-SBM
Published version number	2.1
Applicability	All Sub-markets
Published Date	04/02/2026
Implementation Date	06/02/2026
End Date	-
Terms of variations	Approved Derogation
IsReplacedBy	N/A
Replaces	N/A
Status	Final
Change since last version	Housekeeping changes – Update to sections 3.1, 3.3 and Sub-market guidance.
Description	What? The rule set key elements of how a Sub-Market is designed. These are supplemented by definitions from other rules, to catalogue the different Sub-Markets. How? Core parameters are used to define each Sub-Market. Who? This rule impacts all System Operators. The clearer definitions should benefit all Flexibility Service Providers. When? This rule comes into force in February 2026 Why? This rule aims to aid understanding of how individual Sub-Markets work, as well as how aligned/different they are.