progrunners / UK market data

BM Reports is now Elexon Insights: where GB power data lives

BM Reports (bmreports.com) was switched off on 31 May 2024. The same Balancing Mechanism data — system prices, generation, bid-offer acceptances — is now on Elexon Insights at bmrs.elexon.co.uk. Its API at data.elexon.co.uk is free and needs no key for most datasets. System operator data such as forecasts, carbon intensity and constraint costs comes from NESO on the NESO Data Portal.

Britain publishes more market data than almost anyone, across three systems that overlap. Below the quick answer is a map of which source answers which question, and what bites you once you start pulling it every half hour.

You are looking for	Where it is now
System prices (SSP/SBP), imbalance volumes	Elexon Insights — `bmrs.elexon.co.uk`
Generation by fuel type, demand	Elexon Insights — `bmrs.elexon.co.uk`
Bid-offer acceptances, physical notifications	Elexon Insights — `bmrs.elexon.co.uk`
The same data by API	`data.elexon.co.uk/bmrs/api/v1` — JSON, no key for most datasets
Carbon intensity, forecasts, constraint costs	NESO Data Portal — `neso.energy/data-portal`

Updated 10 November 2026 · Written for developers integrating GB market data. Links re-checked on 10 November 2026.

On this page

Who publishes what in Britain
Three sources, one market
Elexon Insights in practice
Data that only exists here
Traps worth knowing before you start
Where ENTSO-E fits for GB

Who publishes what in Britain

Two organisations matter. Elexon runs settlement and publishes the balancing mechanism data through BMRS. NESO — the National Energy System Operator, formerly National Grid ESO — runs the system and publishes forecasts, carbon intensity and constraint costs.

Both give everything away through an API with no key. Britain is, for once, the easy market.

Three sources, one market

Almost every GB data question resolves to one of three publishers, and picking the wrong one is the most common time sink.

Source	What it holds	Use it for
Elexon Insights `data.elexon.co.uk`	Settlement and balancing: system prices, imbalance volumes, bid-offer acceptances, generation by fuel type, demand.	Anything to do with the Balancing Mechanism or imbalance settlement. This is the modern API and where new work should start.
BM Reports `bmreports.com`	The legacy front end over the same settlement data.	Nothing. Legacy BMRS was switched off on 31 May 2024; the name still ranks and people still land there, but Insights is the only route.
NESO Data Portal `neso.energy`	System operator data: carbon intensity, embedded generation estimates, constraint costs, forecasts, network capacity.	Anything about running the system rather than settling it.

BM Reports is not a second dataset. It was the older window onto the same numbers, and Elexon switched it off on 31 May 2024. Old scripts pointing at bmreports.com no longer get an answer — port them to Insights.

Elexon Insights in practice

The API is open and needs no key for most datasets, which is unusual and pleasant. Responses are JSON, and the filters are consistent across endpoints once you learn the shape.

# System prices for a settlement date
GET https://data.elexon.co.uk/bmrs/api/v1/balancing/settlement/
    system-prices/2026-09-15

# Generation by fuel type, half-hourly
GET https://data.elexon.co.uk/bmrs/api/v1/generation/outturn/
    summary?startTime=2026-09-15T00:00Z&endTime=2026-09-16T00:00Z

Settlement periods, not hours

GB settles in half-hour periods numbered 1 to 48 per settlement day, not in clock hours. On the two clock-change days that becomes 46 and 50. Code that assumes 48 will drop or duplicate an hour twice a year — and because the data still parses, you find out months later when a reconciliation fails.

Single imbalance price

Since P305, GB uses a single imbalance price: both long and short positions settle at the same price for a given period. The EU went the same way: under ACER Decision 18/2020 single imbalance pricing is the rule and dual pricing an exception a TSO has to justify. If you are porting logic from an older dual-price model, check which regime each period and country actually used.

Data that only exists here

Bid-offer acceptances (BOALF) — every instruction NESO issued to every unit, with timestamps. Few markets publish balancing actions at this granularity, and it is the raw material for understanding why a system price landed where it did.
Physical notifications (PN) and MELs — what each unit said it would do and the maximum it could do, per unit, per period.
Carbon intensity — NESO publishes a forecast and outturn carbon intensity API with regional breakdown, widely used and entirely free.
Embedded generation estimates — distribution-connected solar and wind do not appear in metered generation, so NESO estimates them. If your demand numbers look wrong at midday in summer, this is why.

Traps worth knowing before you start

Settlement runs get revised. Data appears as an initial run and is recalculated through II, SF, R1, R2, R3 and RF over months. The number you pulled yesterday is not necessarily the number today. Store the run type alongside the value or your history will drift.
BMU identifiers are not tidy. A single physical plant can map to several BM units, and the mapping changes. Do not build a plant-level model on BMU IDs without a mapping table you maintain.
Times are UTC, the market thinks in local time. Settlement dates are local, timestamps are UTC, and BST shifts the boundary. Convert explicitly at the edge of your system and never in the middle.
Rate limits exist but are undocumented. Pace bulk backfills; pulling a year of half-hourly data with no delay will get you throttled without a clear error.

Where ENTSO-E fits for GB

It mostly does not, any more. After Brexit the Trade and Cooperation Agreement removed the obligation to publish, and all publication for Great Britain on the ENTSO-E Transparency Platform stopped on 15 June 2021. The bidding zone 10YGB----------A still exists in the code lists, but it only returns history up to that date. Northern Ireland is part of the all-island market and is still published.

For anything GB after mid-2021 — prices, balancing actions, unit level data, settlement runs — Elexon and NESO are the only sources. ENTSO-E is useful for GB history and for the continental side of the interconnectors.

We cover the ENTSO-E side in detail in our ENTSO-E API guide.

Frequently asked questions

Do I need an API key for Elexon Insights?

For most datasets, no. The Insights API is open and returns JSON without authentication, which makes prototyping considerably faster than on markets that gate everything behind a token.

Is BM Reports still worth using?

No. It was the legacy interface over the same settlement data and Elexon switched it off on 31 May 2024. Use Elexon Insights.

Why does a settlement day sometimes have 46 or 50 periods?

Because GB settles in half-hour periods and clock changes shorten or lengthen the day. Hard-coding 48 periods is the single most common bug in GB market data code.

What is the difference between Elexon and NESO data?

Elexon publishes settlement and balancing data — what was traded, instructed and paid for. NESO publishes system operation data — carbon intensity, forecasts, constraints, embedded generation estimates.

Does GB use single or dual imbalance pricing?

Single. Both long and short imbalances settle at the same price for a given settlement period, which differs from most continental markets.

Need GB data in production?

We build market data integrations that survive settlement reruns, clock changes and API migrations — live feeds, dashboards and backtesting that respects publication times. If you are pulling Elexon or NESO data into something people trade on, we have done it before.

Get in touch