The deadline for Phase 3 of the Energy Savings Opportunity Scheme (ESOS) is 5 June 2024. If your business is one of the thousands of UK companies in scope of the scheme, you may be seeking the most efficient and cost-effective way to meet your compliance obligations before the deadline. One route to compliance is through international standard ISO 50001, but is it the best option for your business?

What is ISO 50001?

The International Organization for Standardization (ISO) is an official body that sets internationally recognised standards on everything from watch-making to yacht-building. ISO 50001 is the standard for energy management systems.

How ISO 50001 works

The point of having an energy management system (EnMS) is to help organisations do a better job of managing their energy consumption. This might include upgrading equipment or buildings, reducing waste or changing processes. The point of ISO 50001 is to give organisations a framework for these kinds of changes.

As with many ISO standards relating to management systems, the core process for following ISO 50001 is one of continual improvement called Plan – Do – Check – Act. Businesses are expected to keep their energy management policy under continual review, gathering data to assess its effectiveness and changing course if necessary.

ISO 50001 does not impose targets for energy consumption or efficiency. The idea is for the organisation to establish its own baseline and then improve from there.

Why choose ISO 50001 for ESOS compliance?

If your organisation has already achieved ISO 50001 certification, you do not need to carry out an ESOS assessment or appoint an ESOS lead assessor. This might make it seem like a simple route to ESOS compliance. But be warned: it is actually more challenging than carrying out an energy audit.

Under ESOS Phase 3, you do not have to carry out all the energy-saving measures that your audit identifies. But to get ISO 50001 certified, you have to actually implement the best possible energy management system and continually review it for improvement potential. You should be booking annual or half-yearly assessments, in contrast to the ESOS reporting that only needs to be done every four years.

So, no business chooses ISO 50001 as the easy option. They choose it because it is globally recognised as energy management best practice. The obvious benefits include:

  • Financial savings;
  • Lower emissions;
  • Proof that your organisation meets high standards for EnMS.

This proof might be used to comply with mandatory schemes such as ESOS, but it can also be shared with stakeholders, customers and the public.

Getting certification

ISO sets the standards, but it doesn’t perform certification, so you will need to find a certifying body. In the UK there are several bodies who can do this, including BSI (the British Standards Institution) and Lloyd’s Register. Look for one that is accredited by UKAS, the UK’s national accreditation body.

There are two stages to the audit for ISO 50001 certification. Stage 1 is a chance for the auditors to gather and review information on your energy management system. It is done on-site so that they can see the site conditions for themselves and talk to staff as well as looking through the documentation.

Stage 2 is the actual certification stage that determines whether or not your business is ISO 50001 compliant. It is more thorough than Stage 1 and could take many days/weeks and multiple site visits.


If you are considering using ISO 50001 for ESOS compliance, you should get your Stage 1 and Stage 2 audit dates booked in as soon as possible. The more complex your business and the more sites it has, the longer the process will take.

If your business does not pass its Stage 2 audit, you will be told exactly which aspects of your EnMS are non-compliant and given a chance to fix them. But in the meantime, your certification will be delayed. So it really is important to start the process as early as possible.

Giving your organisation the best chance of success

Many businesses treat the Stage 1 audit as a chance to learn of any potential issues and fix them before Stage 2.

Some businesses also book a “pre-audit” before Stage 1 so that they can spot any problems even earlier and address them with corrective measures.

For many organisations, implementing an energy management system in line with ISO 50001 requires resources that don’t exist in-house. So they outsource the job to an accredited Lead Auditor from an external organisation.

Proving ESOS compliance

The official ESOS guidance has a checklist (Appendices A1 and A2) for organisations using ISO 50001 as their route to ESOS compliance. You will need to give details about the organisation and what exactly is covered by the ISO 50001 EnMS: what business assets and activities, where the boundaries of the business are and details of the certification. You will then need to submit documented information about energy savings, which will have been gathered anyway as part of maintaining an ISO 50001-compliant system.

While achieving ISO 50001 certification is a challenge, it will result in your organisation following best practice in the way it manages energy. This is why many organisations choose this option, for the business benefits rather than for regulatory compliance reasons. But you should consider carefully before deciding that this is your best route to ESOS compliance.

If you are considering ISO 50001 as a route to ESOS compliance and would like further advice, get in touch.