Insight
ESOS Phase 4: Turning compliance into an opportunity
For many businesses in the UK, ESOS appears on the agenda every four years. Compliance is essential, but ESOS has the potential to deliver much more than a completed report. The Energy Savings Opportunity Scheme (ESOS) is the UK's mandatory energy assessment scheme for large organisations. It requires qualifying businesses to assess how energy is used across their operations and identify opportunities to improve efficiency. In my experience, the organisations that gain the greatest value from ESOS use it to better understand their operations and make more informed investment decisions, rather than simply meeting their legal obligations.
August 27, 2026
Although the compliance deadline may still feel some way off, businesses that leave ESOS until the last Businesses that leave ESOS until the last minute often limit the value they gain from the assessment.
Good assessments require reliable energy data, engagement with operational teams and an understanding of how energy is actually used across the site. For organisations with multiple facilities, this takes time.
Starting early also allows businesses to identify improvement opportunities before budgets and investment plans have been finalised.
What's changed in Phase 4?
Phase 4 places greater emphasis on what happens after the assessment. Organisations are expected to develop action plans and report progress against commitments, creating a stronger focus on turning recommendations into action.
One manufacturer asked us to review an existing ESOS assessment. By spending time on site, we identified that two factories producing almost identical products were using completely different cooling methods. Aligning those approaches represented a potential annual saving of around £124,000, alongside opportunities to recover waste heat.
That opportunity wasn't found through utility data alone. It came from understanding how the manufacturing process actually worked.
What makes a valuable ESOS assessment?
Not every ESOS assessment delivers the same level of insight. Some rely heavily on desktop analysis and produce long lists of generic recommendations with little guidance on priorities.
The most valuable assessments combine energy data with site visits, process knowledge and conversations with operational teams. The result should be a practical, prioritised roadmap that considers technical feasibility, operational impact and return on investment.
NIRAS Preparation Checklist: ESOS Phase 4
Download our practical checklist to help your organisation prepare for ESOS Phase 4, identify key information early and make sure your assessment delivers value beyond compliance.
Five practical steps to prepare for ESOS Phase 4
If your organisation is beginning to think about Phase 4, here are several practical steps you can take now.
1. Confirm whether your organisation qualifies. Review the latest qualification criteria and understand which parts of the business are included.
2. Start gathering energy data early. Reliable information is the foundation of a good assessment, and identifying gaps now will save time later.
3. Review previous assessments. Which recommendations from Phase 3 have been implemented? Which remain outstanding? Have site operations changed?
4. Engage operational teams. Maintenance engineers, production managers and operators often understand where inefficiencies exist long before they appear in energy reports.
5. Think beyond compliance. Consider how ESOS could support future investment decisions, energy reduction projects and wider decarbonisation plans.
Frequently asked questions about ESOS Phase 4
Does my organisation qualify for ESOS?
Large UK organisations generally qualify if they employ 250 or more people or meet the relevant turnover or balance sheet thresholds. Qualification can become more complex for group structures, so it's worth reviewing eligibility early. You can find out more about qualifying on the government website here.
When should we start preparing?
The earlier, the better. Starting well before the deadline gives you time to gather reliable data, review previous assessments, engage site teams and identify opportunities that may influence future investment decisions.
Do we have to implement every recommendation?
No. ESOS requires organisations to identify opportunities for improving energy efficiency, but it doesn't require every recommendation to be implemented.
What's changed in ESOS Phase 4?
Phase 4 places greater emphasis on action plans and reporting progress against commitments, encouraging organisations to move beyond identifying opportunities and demonstrate how findings are being considered.
What makes a good ESOS assessment?
A valuable assessment combines energy data with site visits, process knowledge and engagement with operational teams. The outcome should be a prioritised, practical roadmap rather than a long list of generic recommendations.
Can ESOS support wider decarbonisation plans?
Yes. Many organisations use ESOS findings to inform energy reduction projects, equipment upgrades and longer-term decarbonisation strategies alongside their compliance obligations.
Get in touch
NIRAS supports organisations with ESOS assessments and engineer-led Energy Opportunity Assessments, helping businesses understand where energy is being used, prioritise opportunities and develop improvement plans that support both operational performance and long-term sustainability. If you'd like to discuss your ESOS Phase 4 preparations, we'd be happy to help.
Adrian Nicholls
Utilities and Process Engineering Manager
Burton upon Trent, United Kingdom
Michael Bannerman
Sustainability Consultant
Burton upon Trent, United Kingdom