Introduction: A Critical Milestone for ESOS Phase 3 Compliance

As the United Kingdom strengthens its environmental compliance framework, the first ESOS Progress Update (PU1) has become a defining milestone for every organisation within ESOS Phase 3. Due on 5 December 2025, PU1 is far more than an administrative task. It marks a significant shift in ESOS, requiring organisations to demonstrate measurable progress in energy efficiency rather than relying solely on audit findings.

"PU1 signals the shift from planning to progress — from intention to implementation.”

The obligation applies to all ESOS participants, even where the Action Plan contained limited or no proposed measures. The Environment Agency expects every organisation to provide an update, ensuring consistent implementation of the strengthened Phase 3 requirements across the UK industry. This reinforces the shared responsibility to reduce energy consumption across buildings, processes and transport.

PU1 encourages organisations to take meaningful steps to improve energy performance and build long-term resilience amid rising energy costs and regulatory expectations. It also helps clarify uncertainties around what counts as progress, especially for organisations navigating complex data systems or multi-site operations.

At Focus Green, we see PU1 as a strategic opportunity rather than a compliance burden. It allows organisations to demonstrate visible progress toward Net Zero while strengthening operational performance. Our consultancy guides clients through every stage of ESOS Phase 3, ensuring that compliance is managed confidently, accurately and efficiently.

With the deadline approaching, organisations that act early will be best placed to demonstrate accountable energy management, strengthen credibility and maintain full compliance.

Understanding the Purpose of Progress Update 1

Progress Update 1 (PU1) is a key part of the strengthened ESOS Phase 3 framework, designed to ensure that organisations move from identifying energy-saving opportunities to demonstrating genuine progress. Its introduction addresses a long-standing gap between audit recommendations and real-world implementation, requiring every ESOS participant to show how they are engaging with the measures set out in their Action Plan, even when those measures were limited.

“The introduction of PU1 reflects a fundamental shift in ESOS: action is now just as important as assessment.”

Unlike earlier phases of ESOS, where compliance largely ended with an audit submission, Phase 3 prioritises ongoing delivery. PU1 is the first formal accountability point, confirming that organisations have begun reviewing, planning or implementing measures. This expectation applies equally to organisations with advanced energy-management systems and those at the start of their efficiency journey, ensuring consistency across all large UK undertakings.

PU1 also helps maintain momentum. After submitting an Action Plan, many organisations face delays due to competing priorities or incomplete data. The update acts as a timely checkpoint, encouraging businesses to remain proactive and ensuring that ESOS remains integrated into day-to-day decision-making rather than becoming a forgotten document.

Another purpose of PU1 is to standardise progress reporting. Submissions must be completed through MESOS using the provided template, ensuring clarity and comparability across sectors. This strengthens the overall integrity of ESOS and allows the Environment Agency to assess national progress more effectively.

PU1 also allows organisations to acknowledge additional improvements identified after the audit. Many businesses discover further energy-saving opportunities as they review their operations, and PU1 ensures these actions are recognised as part of their ongoing progress.

A common misconception is that PU1 is only required when measures have already been implemented. This is incorrect. PU1 is mandatory for every ESOS participant, even if no actions have yet been delivered. In these cases, organisations must clearly explain their position. The Environment Agency expects honesty, not perfection, and values transparency about progress, challenges and next steps.

Viewed within the wider ESOS cycle, PU1 is part of a continuous process of planning, implementation and reporting. It sets the foundation for future updates, supports long-term improvements and prepares organisations for growing stakeholder expectations and regulatory scrutiny.

Ultimately, PU1 strengthens both compliance and practical progress. It ensures organisations are not only aware of their energy performance but are also actively responding to it. For Focus Green clients, PU1 becomes a structured opportunity to demonstrate credible action, reinforce their sustainability strategy and build a strong foundation for all future ESOS submissions.

The Legal Obligation to Submit PU1

Submitting PU1 is a legal requirement for all organisations within the scope of ESOS Phase 3. Government guidance confirms that every participant must submit their update through MESOS by 5 December 2025, regardless of whether any measures have been implemented.

“PU1 is mandatory for every ESOS participant – not only for those that have made progress, but also for those that have not yet begun.”

Failure to meet the deadline is classed as non-compliance and can lead to enforcement action, financial penalties and reputational damage. For organisations operating in competitive or highly regulated markets, missing PU1 can also undermine trust with clients and procurement teams.

Phase 3 reinforces senior leadership accountability. Directors are expected to oversee the delivery of the Action Plan and ensure progress is monitored. PU1 is the formal mechanism that evidences this responsibility.

The update must be submitted using the official MESOS template, as required by the regulator to maintain consistency. Organisations that leave preparation too late often struggle to verify information or gather input from multiple teams. Starting early significantly reduces this risk.

Focus Green works closely with clients to ensure their PU1 is accurate, complete and fully aligned with Government requirements, helping them maintain a strong compliance position ahead of future reporting cycles.

What Must Be Included in PU1

PU1 must provide a clear summary of how the organisation has engaged with the measures outlined in its ESOS Action Plan. For each measure, the organisation must explain whether it has been implemented, is in progress, remains under review or has not yet begun. This allows the Environment Agency to understand the organisation’s position and level of engagement.

Organisations should also report any additional actions identified or implemented after submitting the Action Plan. This ensures that new opportunities discovered through operational reviews or data analysis are captured.

"PU1 must still be submitted even when no actions have been delivered. In these cases, organisations must explain their current status and any reasons for delay. The regulator values honest reporting over incomplete or rushed progress."

Submissions must be completed in the official MESOS template. This standardised format ensures consistency and helps reduce ambiguity. Because PU1 depends on accurate internal information, organisations often need to consult multiple teams, which is why early preparation is recommended.

Focus Green supports this process by reviewing the Action Plan, verifying progress, and preparing a straightforward, compliant PU1 narrative that fully aligns with Government expectations.

How the ESOS Action Plan Links to PU1

The ESOS Action Plan and PU1 are directly connected. The Action Plan sets out the measures an organisation intends to pursue following its audit, while PU1 reports on the progress made against those commitments.

Action Plans are no longer static documents. Under Phase 3, they are expected to guide ongoing energy-efficiency activity, and PU1 ensures organisations revisit these measures and assess what has been achieved. Where new opportunities have been identified, PU1 provides the mechanism to record them.

This link creates a continuous cycle of planning, action and review, strengthening long-term energy management and preparing organisations for future progress updates.

Focus Green helps clients ensure that their Action Plan and PU1 are aligned, realistic and reflective of genuine organisational progress.

Where to Find the Official Templates and Guidance

The official template for Progress Update 1 is available only through the MESOS platform, which must be used for all ESOS Phase 3 submissions. Organisations cannot create their own format or upload alternative documents; the regulator requires PU1 to be completed strictly within the MESOS template to ensure consistency and comparability across all participants. The section on progress updates outlines the purpose of PU1, the expectations around reviewing Action Plan measures and the need for transparent reporting.

Many organisations find it challenging to interpret the guidance alongside the MESOS requirements, particularly when internal responsibilities are split across different teams or sites. Focus Green supports clients by navigating MESOS on their behalf, ensuring the correct template is used and that the submission aligns fully with Government expectations.

Common Challenges Businesses Face When Preparing PU1

Many organisations struggle with PU1 because the required information is spread across different teams, systems, or sites. A common challenge is determining the actual status of each measure in the ESOS Action Plan, especially where records are incomplete or responsibilities are unclear. This can make it challenging to produce a reliable update or verify what has been implemented.

Another frequent issue is uncertainty over what qualifies as “progress”. Some organisations assume they should only report fully completed measures, when in fact the Government expects updates on actions that are still under review or only partly underway. This misunderstanding often leads to under-reporting and weakens the credibility of the submission.

Timing also plays a significant role. Businesses that leave PU1 preparation too late often struggle to gather information, reconcile inconsistencies or seek the internal approvals needed for MESOS. This increases the risk of errors and compromises compliance as the deadline approaches.

Focus Green regularly supports organisations facing these challenges, helping them clarify responsibilities, verify progress and prepare a clear, accurate submission that meets the expectations of ESOS Phase 3.

Why Timely Submission Matters for Compliance and Reputation

Submitting PU1 on time is essential for maintaining compliance with ESOS Phase 3. A late or missing update is treated as non-compliance and can lead to enforcement action, financial penalties and increased scrutiny from the regulator. Beyond the legal implications, timely submission also signals strong governance and demonstrates that the organisation is actively managing its energy performance.

In today’s market, environmental credibility matters. Clients, investors and procurement teams increasingly expect clear evidence of compliance with sustainability regulations, and delays can raise concerns about reliability. A well-prepared, on-time PU1 helps reinforce an organisation’s reputation and demonstrates its commitment to meaningful progress rather than minimal compliance.

Focus Green helps organisations avoid last-minute pressure by establishing clear timelines, coordinating internal contributors, and ensuring PU1 is submitted accurately and on time. This protects both compliance and credibility at a time when environmental performance is under growing scrutiny.

How Focus Green Supports ESOS Progress Updates

Focus Green helps organisations navigate the PU1 process with confidence by reviewing their ESOS Action Plan, verifying the status of each measure and ensuring the update accurately reflects progress. Many businesses struggle to gather consistent information across multiple sites or teams, and we assist by coordinating inputs, resolving uncertainties and confirming what has been implemented or is still under review.

We guide clients through the MESOS platform and complete the official PU1 template in line with Government requirements. Our consultants ensure the submission is clear, coherent and aligned with both the Action Plan and audit findings, reducing the risk of errors or regulatory follow-up.

Beyond the submission itself, we help organisations use PU1 strategically, advising on next steps, future updates and long-term energy-efficiency priorities. This turns PU1 from a compliance obligation into a meaningful part of an organisation’s broader sustainability strategy.

Preparing for the 5 December 2025 Deadline

The first ESOS Progress Update marks a significant shift in Phase 3, requiring organisations to demonstrate real progress rather than simply completing an audit. With the 5 December 2025 deadline approaching, PU1 is an opportunity to show clear engagement with the ESOS Action Plan and strengthen both compliance and credibility.

Preparing a reliable PU1 involves revisiting planned measures, verifying what has happened so far and reporting this accurately through MESOS. Organisations that act early avoid last-minute challenges and are better positioned to deliver a clear, confident submission. A timely PU1 also reinforces good governance and supports wider sustainability commitments, which are increasingly important to regulators, clients and stakeholders.

Focus Green helps organisations prepare PU1 efficiently and accurately, ensuring that every submission meets Government expectations and forms a solid foundation for future ESOS reporting. Early preparation remains the most effective way to stay compliant and demonstrate meaningful progress toward improved energy performance.