Business energy bills hit by £167m in discrepancies

7 October 2026

Business energy bills worth £1.8bn were recalculated by billing validation firm Optima Energy in the first eight months of 2026, with discrepancies totalling £167m, according to the company’s data.

The company has published an open letter calling for changes to the way energy suppliers handle business billing. It has been co-signed by five other firms and submitted as late evidence to the House of Commons Energy Security and Net Zero Committee’s inquiry into business energy.

Optima found that two-thirds of the supplier billing files it examined contained at least one discrepancy. In an eight-week sample this summer, it said a third of 353,067 business bills it validated failed at least one accuracy check.

Late billing was another concern. Over 56,000 invoices worth £246m had been issued more than 12 months after the period they covered since January 2024.

The figures come as billing remains a major source of complaints. Ofgem’s 2024 research found billing was the most common reason businesses complained, accounting for 52% of complaints, while 47% of businesses that had complained said the issue had not been resolved by their supplier.

Billing was also the largest category of disputes handled by the Energy Ombudsman in 2025, accounting for 56% of cases.

Optima is also warning about preparations for market-wide half-hourly settlement, which is due to begin in May 2027. It said more than a quarter of the business bills it processes are still based on estimated meter readings.

Optima managing director Sebastien Weyland comments:

“As a bill validation software and bureau service provider, we are at the forefront of this issue. We see every discrepancy, and we see them increasing, with billing formats getting worse, not better.”

The letter calls for independent checks on billing accuracy, standardised machine-readable invoice data and consistent application of the 12-month back-billing principle.

It also calls on Ofgem and the government to extend back-billing protections to all non-domestic customers, introduce compensation for supplier-caused errors and independently assess suppliers’ readiness for half-hourly settlement.