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ESOS phase 4: qualification criteria, energy audit and deadline

ESOS is a mandatory energy assessment every 4 years for large UK undertakings and their groups. Here is how to check whether you qualify for phase 4 and what the assessment involves.

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Qualification on 31 December 2026

You qualify for phase 4 if, on 31 December 2026, you have 250 or more employees, or a turnover above £44 million and a balance sheet total above £38 million. A group qualifies if at least one UK member is large. If you qualified before but not for phase 4, tell your regulator.

The steps of an ESOS assessment

Significant energy consumption must cover at least 95% of the total. Audits use 12 months of verifiable data starting no earlier than 6 December 2022 and include site visits. ISO 50001 counts if issued after 5 December 2023 and valid on 5 December 2027.

An approved lead assessor signs off unless ISO 50001 applies or consumption is under 40,000 kWh. A board level director approves the notification, filed on MESOS by 5 December 2027.

Frequently asked questions

What is new in ESOS phase 4?

Progress against earlier action plan commitments must now be reported, with reasons where they were not met. DECs and Green Deal assessments are no longer accepted. A voluntary net zero assessment can be added using PAS 51215-1:2025 and PAS 51215-2:2025.

Is there still something to do for ESOS phase 3?

Yes. Phase 3 participants must submit an annual action plan progress update on MESOS by 5 December 2026, signed off by a board level director.

Who enforces ESOS?

It depends on your registered office: the Environment Agency, Natural Resources Wales, the Northern Ireland Environment Agency or SEPA, with DESNZ for mainly offshore organisations. They can impose civil sanctions, including financial penalties.

For developers and agents

Embed / API / MCP

Connect this base to Claude, Cursor, ChatGPT or your own app. Each API or MCP request costs €0.10, charged to your Kopik credit (not charged if nothing is found). You need an API key: create one from your dashboard.

MCP for your agents

This base's MCP server URL (tools ask_base and search_base):

MCP URL
https://kopik.io/api/mcp?base=uk-business-carbon-energy-waste-compliance
Claude Code, Cursor and other clients
Claude Code
claude mcp add --transport http kopik-uk-business-carbon-energy-waste-compliance "https://kopik.io/api/mcp?base=uk-business-carbon-energy-waste-compliance" --header "Authorization: Bearer kpk_…"
JSON config (mcpServers)
{
  "mcpServers": {
    "kopik-uk-business-carbon-energy-waste-compliance": {
      "url": "https://kopik.io/api/mcp?base=uk-business-carbon-energy-waste-compliance",
      "headers": {
        "Authorization": "Bearer kpk_…"
      }
    }
  }
}

REST API for your apps

mode is "answer" (written answer + sources) or "passages" (raw passages only). Add an optional maxPriceCents to cap the price: if the base costs more, the call is refused and nothing is charged.

curl
curl -X POST https://kopik.io/api/v1/bases/uk-business-carbon-energy-waste-compliance/query \
  -H "Authorization: Bearer kpk_…" \
  -H "Content-Type: application/json" \
  -d '{"question": "Your question here", "mode": "answer"}'

Getting started

  1. Create a key in your dashboard and top up your credit.
  2. Replace kpk_… with your key.
  3. Full details (responses, errors, JS and Python examples): developer docs.