ISO 50001 (Energy Management Systems – EnMS): is it the best route to ESOS compliance?

The government’s Energy Savings Opportunity Scheme (ESOS) is now well into its third phase (running to 5th December 2023), and the thousands of UK businesses in scope of the scheme will want to find the most efficient and cost-effective way to comply with the scheme. One of the routes to compliance is through international standard ISO 50001, but is it the best option for your business?

How ISO 50001 works

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, setting out a framework to help businesses create an effective energy management system.

To follow ISO 50001, you will have to gather accurate data on energy use in your organisation, develop a policy to improve energy efficiency and set targets in line with that policy. ISO 50001, like many other ISO standards related to management systems, is based on a continual improvement model. So, it requires an organisation to keep measuring the results of its energy efficiency measures, continually evaluate the success of its policy and keep improving. There is detailed guidance on how best to do this, including how to carry out an energy audit. In its very basic form and principles, ISO 50001 is a framework of: plan – do – act – check.

Some organisations choose to implement ISO 50001 simply because it is globally recognised as best practice for managing their organisation’s energy use. Others choose to get certified so they can prove to stakeholders and external bodies that they are meeting certain standards. If your company wants to use ISO 50001 as a route to ESOS compliance, it will need certification.

For many organisations, the skillsets required to successfully implement an ISO 50001 Energy Management System can place a strain on staff if undertaken in-house. Therefore the outsourcing of an external support is typically used, with accredited Lead Auditor in IS0 50001.

Getting certification

ISO sets the standards, but it doesn’t perform certification. 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.

ISO 50001 is applicable to any organisation no matter what its type or size, but the process of implementing a standard-compliant energy management system and then getting it certified will obviously vary depending on the specifics of your business. The more complex your business and the more sites it has, the longer the process will take.


If you choose ISO 50001 as your route to ESOS compliance, it is important to allow enough time before the phase 3 deadline of 5 December 2023. It’s a good idea to choose and contact your certification body early in the process and get your audit dates booked in. There are two stages to the audit. 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.

For many businesses, Stage 1 is a chance to learn of any potential issues that could jeopardise compliance and take the opportunity to 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.

Once you’ve gained your certification, you will need to book in regular audits to check that your energy management system is still operational and effective. These are usually yearly or twice-yearly.

Of course, some businesses do not pass their Stage 2 audit. The auditor’s report will be clear on exactly which aspects of the energy management system are non-compliant, so you can work to bring them into compliance, but in the meantime your certification will be delayed. This is one of the reasons why it’s important to start the process early if you want to use ISO 50001 for ESOS compliance. Unlike with the conventional route to ESOS compliance, you don’t need to have a 12-month reference period that spans the qualification date of 31 December 2022, which means you don’t need to wait until this time to see if you comply.

Why choose ISO 50001 for ESOS compliance?

If your organisation is fully covered by ISO 50001, you do not need to carry out an ESOS assessment or appoint an ESOS lead assessor to review any of your paperwork. You just have to tell the Environment Agency (which administers ESOS) that you are compliant.

However, this doesn’t mean that anybody sees ISO 50001 as an easy route to ESOS compliance. It is actually more challenging than conventional ESOS reporting in many ways. While ESOS simply requires you to report on energy use and efficiency and then offers suggestions for improvement, ISO 50001 actually requires you to implement the best possible energy management system and then continually review it for possible ways to make it better.

The biggest benefit of ISO 50001 is precisely what makes it the less easy option: it will result in your organisation following best practice in the way it manages energy, and having the certification to prove it. You will save money through lower energy costs and have documented evidence that the business takes sustainability seriously. This is why, for many companies, choosing ISO 50001 is less about regulatory compliance and more about the provable business benefits and going the step beyond solely adhering to compliance.

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