UK Energy Supplier Scores 2026: KT Score League Table

Octopus Energy tops the KT Score for April to June 2026 with 76 out of 100, level with E.ON Next on 76 and separated by a lower dispute rate. Octopus had 21.07 disputes accepted by the Energy Ombudsman per 100,000 domestic accounts, the lowest of the eight suppliers reported individually. Scottish Power had the highest at 65.10, more than three times the Octopus rate.

The KT Score league table, April to June 2026

Scored as 100 minus the dispute rate for the complaints component, and the star rating as a percentage of five for the service component. Where two suppliers score the same, the lower dispute rate ranks higher, which is the tiebreak Citizens Advice applies in its own table. Sources: Energy Ombudsman Disputes Data Q2 2026 and Citizens Advice domestic supplier star rating.

Which energy supplier gets the most complaints?

Scottish Power. It had 65.10 disputes accepted by the Energy Ombudsman per 100,000 domestic accounts in Q2 2026, the highest of the eight suppliers the Ombudsman reports individually. British Gas followed on 54.90 and EDF Energy on 48.84. At the other end, Octopus Energy had 21.07, Utilita 21.41 and E.ON Next 22.72.

The gap matters more than the ranking. Scottish Power's rate is 3.1 times the Octopus rate. Put differently, for every 100,000 customers, Scottish Power generated about 44 more unresolved disputes in a single quarter than Octopus did.

These counts are not all complaints. The Ombudsman only accepts a case after the supplier has failed to resolve it within eight weeks or has issued a deadlock letter. A supplier that handles complaints well at the first attempt will show a low figure here even if its total complaint volume is high. That is a different measure from the one Ofgem publishes, which counts every complaint a supplier receives.

Which is the worst energy supplier for service?

On these two measures, Scottish Power scores lowest overall at 44 out of 100, held down by the highest dispute rate in the set. British Gas is next at 48, with the lowest Citizens Advice star rating of the eight at 2.61 out of five.

Utility Warehouse at 54 and EDF Energy at 55 sit close together but for different reasons. EDF has the worse dispute rate of the two at 48.84 against 45.38, while Utility Warehouse has the worse star rating at 2.63 against 2.96. A single number hides that, which is why both components are shown in the table above.

Octopus Energy against British Gas

This is the comparison people search for most often, and on complaints and service the gap is wide. Octopus Energy scores 76 against British Gas on 48. Octopus had 21.07 Ombudsman disputes per 100,000 accounts against 54.90 for British Gas, so British Gas generated 2.6 times the rate of unresolved disputes. On the Citizens Advice rating Octopus scored 3.67 against 2.61.

Two caveats are worth stating. British Gas is the largest domestic supplier in Great Britain and a long legacy book brings older meters, more complex billing histories and more inherited problems, none of which the rate adjusts for. And neither measure says anything about price. A supplier can rank well on complaints and still not be the cheapest tariff for a given household.

What the two measures actually count

Energy Ombudsman disputes per 100,000 accounts

The Ombudsman publishes quarterly data for suppliers with more than one million consumer accounts. The figure counts domestic cases raised by consumers that the Ombudsman accepted, divided by the supplier's domestic account base and expressed per 100,000. It excludes disputes the supplier settled directly before the Ombudsman stage.

Across its Q2 2026 report, billing was the most common dispute category, accounting for 58 per cent of accepted cases in the first half of 2026. Billing was the largest category for every one of the eight suppliers, ranging from 47 per cent of Utilita's cases to 63 per cent of Utility Warehouse's.

Citizens Advice star rating

Citizens Advice rates suppliers with more than 25,000 accounts from one to five. The rating weights complaints to third parties at 35 per cent, ease of contact at 30 per cent, billing and metering at 25 per cent, and customer commitments at 10 per cent. Its April to June 2026 wave put the median at 3.4, up from 3.26 the previous quarter, with median call waiting times falling from 77 to 68 seconds.

Because the Citizens Advice complaints component draws partly on Energy Ombudsman data, the two measures in the KT Score overlap to that extent. The overlap is stated here rather than hidden: it means a supplier with a poor dispute record is penalised twice, once directly and once through its star rating.

What this score does not tell you

It is not a price comparison. Nothing in either data set measures tariffs, standing charges or exit fees, and a supplier near the top here may still be more expensive than one near the bottom.

It is not a measure of total complaints. Both sources capture complaints that reached a third party, so a supplier that resolves problems quickly at first contact looks better than one that does not, regardless of how many problems arose.

It is a snapshot. Both data sets are quarterly and both move. The Citizens Advice median rose in each of the last two quarters, so a supplier can slip in the table while improving in absolute terms simply because others improved faster.

When this table updates

The Energy Ombudsman publishes quarterly disputes data and Citizens Advice publishes a quarterly star rating. This table is rebuilt when both are available for the same quarter, so it moves one quarter behind the calendar. The current edition covers April to June 2026.