P434 Unmetered Supplies (UMS)– what it is & how to comply

P434 is an industry change by Elexon as a precursor to Market-wide Half Hourly Settlement (MHHS), which means that all non-half hourly unmetered supplies must move to Half Hourly (HH) settlement by October 2025. 

Elexon is the industry regulator and administers the settlement of electricity between generators and suppliers. 

They’re currently running the biggest change to the UK’s electricity settlement: Market-wide Half Hourly Settlement (MHHS), where all electricity supplies will move to Half Hourly (HH) settlement 

And MHHS includes all the ~32k Unmetered supplies in the market.

Why is P434 happening?

P434 was put in place to make the wider MHHS Programme run smoothly.

MHHS is happening to provide a better settlement & balancing of the UK’s grid and increase our national ability to hit Net Zero.

When is P434 happening?

The deadline for unmetered supplies to move to Half Hourly settlement is 22nd October 2025, as per the MHHS programme milestone M11.

Who does P434 affect?

P434 will typically affect councils and local authorities but some private businesses too.

Anyone with Unmetered Supplies (UMS) equipment must maintain an inventory detailing their UMS equipment.

Common examples of unmetered equipment include:

• Street lighting
• Traffic signals
• Telecom cabinets
• Public signage (e.g., billboards, bus shelters)
• CCTV cameras

This inventory must be moved from the Non-Half Hourly settlement to the Half Hourly settlement as part of the P434 change.

Both parties will need to work their UMS portfolios from Non-Half Hourly to Half Hourly settlement through a change of measurement class (CoMC) ahead of the September 2025 deadline.

What needs to happen to comply with P434?

You must ensure a Meter Administrator (MA) is in place.

It will be required as part of the Change of Measurement Class (CoMC) activity.

The MA will be in place already for HH Supplies, however, smaller NHH UMS portfolios may not have one.

The MA, such as Stark, will assist with all aspects of the Change of Measurement Class (CoMC) and ongoing data service required to achieve P434.

What happens to Unmetered supplies after the P434 change of measurement class?

Once unmetered supplies are being settled under Market-wide Half Hourly Settlement from October 2025, an Unmetered Supplies Data Service (UMSDS) agent will engage in providing the Half Hourly data for settlement.

Stark will be performing this service as well.

Can Stark help with P434 & Unmetered supplies?

Yes. We are the only Meter Administrator in the UK with ISO9001:2015 with proprietary software for precision calculations & reporting for unmetered supplies.

We also perform the UMSO role through Stark Infra for connection agreements for unmetered equipment. 

Plus we are qualified for all roles in Market-wide Half Hourly Settlement.

We do it all.  

Summary

With unmetered supplies, the settlement objective is the same: Market-wide Half Hourly Settlement. 

P434 ensures that Unmetered supplies are moved to Half Hourly Settlement in good time, ahead of the main metered migration under Market-wide Half Hourly Settlement. 

All UMS must move to HH settlement by 22nd October 2025 & must have a Meter Administrator.

As a Meter Administrator, we are able to support our customers through P434, the change of measurement class and beyond through MHHS as UMSDS.