ESOS Progress Update 2026: Can You Show What Changed?

The second annual progress update for organisations that qualified for Phase 3 of the Energy Savings Opportunity Scheme is due by 5 December 2026.

The deadline matters, but it is not the most useful part of the exercise.

The real question is whether your organisation can explain what has happened since its ESOS action plan was submitted. Which measures were implemented? Which were delayed or changed? What energy savings have been achieved or are expected? How were those estimates calculated? And, perhaps most importantly, what should happen next?

For many businesses, the difficult gap is not between knowing the deadline and submitting the update. It is the gap between an action written in a plan and a measurable change on an operating site.

This guide explains the current Phase 3 progress-update requirements and how organisations can use the process to create something more valuable than a compliance record: a clearer view of their buildings, their priorities and the actions most likely to produce credible savings.

This article provides general information, not legal or regulatory advice. Organisations should check the current government guidance and obtain appropriate ESOS support for their circumstances.

What is the December 2026 ESOS deadline?

ESOS is a mandatory energy-assessment scheme for large UK organisations that meet its qualification criteria. Under the Phase 3 requirements, qualifying participants were required to submit an action plan following their compliance notification and then provide annual updates on their progress.

The first Phase 3 progress update was due on 5 December 2025. The second and remaining Phase 3 progress update is due on 5 December 2026.

According to the current government guidance, this update relates to the reporting period from 6 December 2025 to 5 December 2026. It must be approved by the required board-level director or equivalent and submitted through the Manage your Energy Savings Opportunity Scheme reporting service, known as MESOS.

If an organisation qualified for Phase 3 but has not submitted its action plan, the government guidance advises contacting the Environment Agency.

The authoritative requirements and any subsequent changes should always be checked on the UK Government ESOS guidance page before submission.

What does an ESOS progress update need to show?

The progress update is intended to record movement against the organisation’s action plan. It is not simply a statement that energy efficiency remains an objective.

The government’s Phase 3 guidance requires relevant information about measures implemented during the reporting period, including an estimate of the energy savings achieved or expected and the method used to produce that estimate. Measures that were not included in the original action plan may also be reported.

In practical terms, the organisation needs a defensible account of:

• which energy-saving measures were implemented;
• when implementation took place;
• the estimated saving during the relevant period;
• the units used to express that saving;
• the method and assumptions behind the estimate;
• actions that changed, moved or did not proceed; and
• any additional measures delivered outside the original plan.

The progress update must receive the appropriate director-level sign-off. That makes the quality and clarity of the underlying information important. Senior decision-makers should be able to understand what is being reported, where the figures came from and whether the next proposed actions remain commercially sensible.

Why an action plan can drift away from the real building

Commercial buildings do not stand still while an action plan is being implemented.

Opening hours change. Tenants move. Areas are repurposed. Equipment is replaced or isolated. Controls are overridden. Maintenance issues emerge. Occupancy rises or falls. Production schedules change. Energy prices move. Projects that originally looked straightforward encounter budget, procurement or access constraints.

These changes can affect both the expected saving and the method used to evaluate it.

For example, a reduction in gas consumption following a heating-controls change may look impressive until the comparison period is examined and found to have been significantly warmer. An electricity-saving project may appear to have underperformed even though the site increased its operating hours. A project described as complete may not yet be producing the expected outcome because staff are still relying on manual overrides.

None of this automatically means the original action was wrong. It means the site context needs to be documented.

An estimate without context can create false confidence. A technically sound measure supported by a clear baseline and a transparent explanation is far more useful than a larger claim that cannot be defended.

Compliance evidence and operational evidence are not identical

An ESOS progress update has defined reporting requirements. Operational energy management asks a wider set of questions.

Compliance evidence may establish that a measure was implemented and provide an estimate of its saving. Operational evidence looks at whether the change is still working, whether the original assumptions remain valid and whether another intervention should now take priority.

Useful operational questions include:

• Is the equipment operating according to the intended schedule?
• Have temporary overrides become permanent?
• Does the control strategy still match occupancy and operating hours?
• Has a maintenance fault affected performance?
• Are heating and cooling operating against each other?
• Has the measure moved demand elsewhere in the building?
• Can the saving be separated from weather, production or occupancy changes?
• Is the site team clear about who owns the new setting or procedure?

This is where a physical understanding of the building becomes important. Bills and portfolio data provide valuable signals, but they do not always identify the plant, control setting or operational routine responsible for a change.

Start by rebuilding a clear evidence trail

Organisations preparing their second progress update should not wait until the submission date to reconstruct twelve months of activity.

A practical evidence trail can be built in five stages.

1. Return to the original action plan

List each committed measure and its proposed implementation date. Identify what was reported in the first progress update so that the second update describes genuine subsequent progress rather than repeating the same activity.

Record whether each action is complete, in progress, delayed, replaced or no longer considered appropriate. Where a decision changed, retain a short explanation. A revised decision supported by current evidence is more credible than silently carrying forward an outdated action.

2. Confirm what happened on site

Speak with the facilities, operations, maintenance and site teams responsible for the relevant buildings. Purchase orders and completion certificates can show that work was commissioned; they do not necessarily confirm how it is operating today.

Check commissioning records, control settings, maintenance logs, installation dates and any subsequent faults or adjustments. For operational measures, confirm that the revised procedure is still being followed.

3. Define a suitable baseline

The baseline should represent energy use before the measure, with enough information to explain relevant differences between the baseline and reporting periods.

Depending on the project, this may require consideration of:

• external temperature or degree days;
• opening and closing times;
• occupancy levels;
• production or sales volumes;
• floor area or zones in use;
• equipment additions or removals;
• changes in tariffs, where financial savings are discussed; and
• unusual closures, faults or exceptional events.

The objective is not to produce a perfect laboratory experiment. It is to use a method that is proportionate, transparent and appropriate for the measure being reported.

4. Calculate the estimate and record the method

Use the unit and methodology required by the current ESOS guidance. Keep the calculation, source data and assumptions together so another person can understand how the estimate was reached.

Avoid presenting precision that the available evidence cannot support. Where the result is an estimate, describe it as an estimate. If there are material limitations, record them.

5. Agree the next action and its owner

The progress update looks backwards, but the management value comes from deciding what happens next.

For every incomplete or newly identified measure, record:

• the next practical action;
• the person or team responsible;
• dependencies or information still required;
• the expected decision or implementation date; and
• how the eventual result will be measured.

This turns reporting into an active energy-management process rather than a once-a-year search for documents.

Common weaknesses to look for before submission

Even when organisations have implemented meaningful projects, the supporting record can be weaker than the work itself.

Reporting installation rather than performance

“Equipment installed” describes an activity. It does not describe the outcome. Wherever the data allows, explain the operational change and the method used to estimate its effect.

Comparing unlike periods

Simple year-on-year comparisons may be distorted by weather, occupancy, production, opening hours or estate changes. These factors should be considered when they materially affect the conclusion.

Using supplier projections as the only evidence

Pre-installation projections help build a business case, but they are not the same as post-implementation evidence. Check whether actual operating data supports the original assumptions.

Losing sight of low-cost operational measures

Capital projects are easier to record because they generate quotations, orders and completion documents. Scheduling changes, control corrections, shutdown procedures and maintenance improvements can be less visible even when they matter. Give operational actions an owner and retain evidence of when they changed.

Carrying forward actions that no longer suit the site

An action plan should not force an organisation to pursue a poor investment. If site conditions, costs or priorities have changed, document the evidence and reassess the option.

Treating director sign-off as a final administrative step

The responsible director should have a clear summary of the progress, estimates, methods, limitations and next priorities. The sign-off conversation is an opportunity to reconnect energy performance with operational risk and capital planning.

How an Onsite Discovery Assessment can support the process

Green Wing’s Onsite Discovery Assessment is designed to understand what an operating building is actually doing with energy.

We inspect major loads, plant and controls, and consider how schedules, occupancy and daily routines affect performance. The aim is to separate observable operational improvements from technology opportunities that require investment or further evidence.

For an organisation preparing or strengthening its energy action programme, this can help to:

• verify whether completed measures are operating as intended;
• identify changes in the building that affect previous assumptions;
• locate avoidable waste that portfolio-level data cannot explain;
• distinguish quick operational fixes from capital projects;
• identify where more monitoring or investigation is required; and
• create a clearer measurement route before the next intervention.

The findings can then be developed into a Discovery Assessment Report and Roadmap. Opportunities are ranked by likely value, payback, complexity, dependencies and the proposed method for measuring the result.

Where ESOS evidence is required, relevant findings and reports can be reviewed by a qualified ESOS assessor. Green Wing’s focus remains the practical outcome: making sure the work is useful to the people responsible for the site as well as those responsible for compliance.

From annual reporting to continuous improvement

The strongest energy programmes do not begin and end with a reporting deadline.

They use a repeatable cycle:

1. Observe how the site is operating.
2. Identify and rank the opportunities.
3. Agree the baseline and measurement method.
4. Implement the appropriate action.
5. Verify the result.
6. Review what should happen next.

This matters particularly across multi-site estates. A control issue found at one property may exist elsewhere, but it should not simply be assumed. The finding can be used to create a targeted check across comparable sites, allowing the organisation to identify where the same action is suitable and where local conditions differ.

Energy Optimisation as a Service extends this approach beyond a one-off assessment. Regular review, prioritised next actions and savings verification help prevent settings, habits and performance from drifting after a project is completed.

A practical checklist for the 2026 progress update

Before the 5 December deadline, confirm that your organisation has:

• checked the latest official ESOS guidance;
• reviewed the original Phase 3 action plan and first progress update;
• identified measures implemented during the relevant reporting period;
• included any additional qualifying measures not in the original plan;
• confirmed implementation dates and current site status;
• estimated the relevant energy savings;
• documented the method, data and assumptions used;
• considered material changes in weather, occupancy or production;
• recorded delays, substitutions and changed decisions clearly;
• secured the required director-level review and approval; and
• allowed sufficient time to submit through MESOS.

If the evidence behind an action is incomplete, identify the gap now. A meter-data request, site conversation or controls check is easier to complete in September or October than during the final days before submission.

The deadline is not the difficult part

Submitting an ESOS progress update is a defined task. Demonstrating that planned measures became real, measurable improvements requires stronger coordination between sustainability, finance, operations and site teams.

That coordination creates value beyond compliance.

It shows which actions worked. It prevents weak projects from being repeated. It gives decision-makers a clearer basis for allocating capital. And it helps the organisation move from a static list of opportunities to an active, evidence-led programme.

If you need a clearer view of how your buildings are operating, Green Wing can carry out an Onsite Discovery Assessment and turn the findings into a ranked Discovery Assessment Report and Roadmap.

Arrange an Energy Review to discuss your estate, or request a sample Roadmap to see how operational and technology opportunities are prioritised and measured.

Arrange an Energy Review Start with a free 15-minute discovery call.