The typical large UK business identified £100,000 a year of energy savings in its ESOS assessment, according to Environment Agency data. A year after publishing its action plan, it had delivered just over half of the measures on the list. The rest are still sitting in a spreadsheet, and from December they’ll be back on the public record.

Fact: Only 56% of the 26,562 measures promised in ESOS 3 action plans had been done. One in six companies has implemented none of what they said they would do.

What is ESOS, and where does this data come from?

The Energy Savings Opportunity Scheme (ESOS) is the government’s mandatory energy audit for large organisations: any UK business with 250 or more staff, or a turnover above £44m and a balance sheet above £38m, according to GOV.UK’s ESOS guidance.

In Phase 3, every participant had to publish an action plan by 5 December 2024 and how it would save on energy, then file a progress update a year later saying what it had done and the impact.

The Environment Agency publishes those updates on data.gov.uk. The latest release, dated 5 June 2026, covers 5,609 progress updates and 30,481 measures.

How much of what was promised has been delivered?

Less than you’d hope.

  • Only 56% of promised measures have been implemented. The other 44% have not happened yet.
  • One in six companies (18%) has implemented none of its measures. Only 29% have done all of them.
  • The biggest savings are the least likely to get done. Heat pumps (37% delivered) and solar PV (46%) lag far behind site consolidation (76%) and LED lighting (59%).
  • LED lighting is the most popular measure by a wide margin, with more than 5,400 planned.
  • Few companies raised their ambitions. Only 852 (15%) added any new measures after their action plan.
  • More than 600 progress updates arrived after the 5 December 2025 deadline, 312 of them in 2026.

GOV.UK’s Phase 3 compliance guidance states that action plan and progress update failures ‘do not currently result in any penalties but may be identified through public disclosure’. The only sanction for not doing what you said is that everyone can see it.

Why do the biggest savings stall?

The cheaper and simpler a measure, the more likely it gets done. The measures that save the most are the ones businesses keep putting off.

Each dot is a measure type: typical four-year saving per measure against the share implemented. Source: Environment Agency, ESOS Phase 3 progress update 1 public data, 5 June 2026. Site consolidation is the exception (the green dot). It saves a lot and it gets done, because closing a site cuts rent and rates as well as energy, so nobody has to win an argument about payback. The data points to four reasons everything else stalls.

  1. Capital cost. Heat pumps and voltage optimisation need upfront investment. Funded models and power purchase agreements can take the cost off the balance sheet.
  2. No clear owner. ESOS gets treated as a compliance exercise. Once the report is filed, nobody is accountable for delivery.
  3. No data to prove the case. Fewer than one in three reported savings were backed by an energy audit. The rest were estimates, which is a weak position from which to ask for capital.
  4. Grid constraints. Electrifying heat and fleet can need extra capacity from the network operator, and that takes time.

The ranking below orders measure types by typical saving: the median estimated saving per measure over the four years to 5 December 2027, as stated in company action plans. Medians partly reflect company size, so treat them as a guide to scale, not a promise.

1. Voltage optimisation

Saves: about 160,000 kWh over four years, worth £29,000 at 18p per kWh.

Delivered: 48%. Costs: £5,000 to £10,000 for a supply up to 200 kVA, £15,000 to £40,000 for 500 kVA to 1 MVA. A £25,000 unit pays back in about three and a half years.

Most sites receive power at a higher voltage than their equipment needs, and the surplus is lost as heat. A voltage optimiser trims it. Biggest typical saving in the data, yet fewer than half of planned units are in. It's a capital project, and that's where ESOS plans go quiet.

2. Heat pumps

Saves: about 142,000 kWh over four years, worth £26,000.

Delivered: 37%.

Costs: around £1,530 per kW for air source and £2,690 per kW for ground source, according to the BEIS non-domestic heating evidence update (November 2022). A 100 kW air source system is about £153,000, three to five times a gas boiler.

Lowest delivery rate of any measure. Cost, disruption and grid capacity are the blockers. Check capacity before the boiler fails and makes the decision for you.

3. Consolidate your estate

Saves: about 130,000 kWh over four years, worth £23,000.

Delivered: 76%.

Costs: nothing to install.

The cost is the lease exit and the move. Best delivery rate in the data, because the property case makes the energy case. Attach energy measures to decisions the business is already making, like a refit or a lease break.

4. Solar PV

Saves: about 110,000 kWh over four years, worth £20,000.

Delivered: 46%.

Costs: £1,256 per kW for a 10 to 50 kW system in 2024/25, according to DESNZ solar PV cost data.

A 30 kW array is about £38,000 and pays back in around seven years. Zero upfront under a power purchase agreement. Cost is the usual excuse and the least necessary one. If you export, the rate you're paid varies widely between suppliers.

5. Compressed air, motors and variable speed drives

Saves: about 83,000 kWh over four years, worth £15,000.

Delivered: 58%. Costs: a leak survey is £500 to £1,500. A variable speed drive is £1,500 to £5,000 installed.

A single 3mm leak wastes over £1,000 a year, and slowing a fan or pump by 20% can halve its running cost, according to the Carbon Trust. Delivery is above average because engineers own these jobs and don't need a board paper.

6. Fleet and travel

Saves: about 79,000 kWh over four years, worth £14,000.

Delivered: 53%.

Costs: telematics £10 to £25 per vehicle per month, driver training £50 to £150 per driver.

Electric vans cost a few thousand more than diesel, but fleets replace on a cycle anyway. Transport counts towards ESOS, and for distribution firms it's often the largest share. Driver training is cheap and easy to evidence from fuel card data.

7. Heating, boiler and HVAC upgrades

Saves: about 56,000 kWh over four years, worth £10,000.

Delivered: 59%. C

osts: lowering flow temperature is free.

Pipe insulation is £10 to £20 per metre. A commercial boiler replacement is £10,000 to £40,000. Boiler replacement was the most common measure added in 2025, which suggests businesses wait for failure. Heating costs rise about 8% per 1°C of overheating, so fix the controls first. And price a heat pump before you buy another gas boiler.

8. Metering and monitoring

Saves: about 52,000 kWh over four years, worth £9,400.

Delivered: 43%.

Costs: £300 to £800 per sub-meter installed, £50 to £200 per site per month for monitoring. One of the least delivered measures and the one that matters most. Without half-hourly data you can't find waste or prove anything else worked. Fewer than one in three reported savings were backed by an audit.

9. BMS and controls

Saves: about 40,000 kWh over four years, worth £7,200.

Delivered: 57%.

Costs: £2,000 to £5,000 to recommission an existing BMS.

A new one is £20,000 to £60,000 for a mid-sized building. Time clocks and setpoints cost nothing. If a site uses almost as much at 3am as at 3pm, the controls are the first thing to check.

10. Staff behaviour and training

Saves: about 37,000 kWh over four years, worth £6,700.

Delivered: 52%.

Costs: £1,000 to £3,000 for a switch-off campaign with energy champions. The Carbon Trust puts behavioural savings at up to 5% of the bill. Campaigns only last if staff can see the results, so pair them with monitoring.

And LED lighting: the most popular measure of all

Saves: about 21,000 kWh over four years, worth £3,800.

Delivered: 59%.

Costs: £40 to £120 per fitting installed.

Payback two to four years, the fastest capital measure here. Most popular measure by far, with more than 5,400 planned. Smaller savings per project because the obvious areas are done. If you haven't, start here.

The full ranking at a glance

Worked example: what the gap costs a typical ESOS business

The average business in the Phase 3, reported a saving opportunity of 600,000 kWh and £100,000 a year. Apply the 56% delivery rate and around £56,000 a year has been saved per business. The business has already paid for the audit that found it. Scale that median across the 5,609 businesses in the data and the undelivered savings come to roughly £250m a year. By volume, more than a third of the savings promised in Phase 3 action plans sit in measures that have not been implemented.

The savings ESOS plans miss entirely

ESOS is about using fewer kilowatt hours. But a large share of a business energy bill has nothing to do with how much you use, and it can often be cut faster than any efficiency project, with no capital spend.

  • Reduce your supply capacity. Many sites pay for far more agreed capacity (measured in kVA) than they ever draw. Cutting it to match real demand lowers the fixed network charge on every bill.
  • Claim the tax breaks you are entitled to. The Climate Change Levy costs 0.801p on every kWh of electricity and gas from 1 April 2026, according to GOV.UK’s CCL rates. Businesses with a climate change agreement get a 92% discount on electricity and 89% on gas. You can check all government subsidies here
  • Buy better. Contract timing, fixed or flexible pricing, and supplier choice can move costs more than a year of efficiency measures.

What to do before 5 December 2026

The second ESOS progress update is due by 5 December 2026, and the Phase 4 compliance deadline follows on 5 December 2027, according to GOV.UK. Every measure still marked ‘not implemented’ will be published again. If your business is in ESOS, we’d do four things this quarter. Revisit the action plan and pick the two or three highest-value measures you haven’t started. Put metering in place so you can evidence the savings. Review your supply capacity and contracts for savings that need no capital. And price the funded options for solar and heat pumps before assuming you can’t afford them. If you’re not in ESOS, the lesson still applies. The businesses that save the most follow through on the bigger projects.

How Purely Energy can help

We’ll review your sites, your half-hourly data and your contracts, and show you which of these measures would make the biggest difference to your bill, including the ones ESOS never looks at. See how it worked for other clients in our case studies, or ask for a free review.