Inspectors from consumer markets watchdog ACM visited the offices of the three biggest Dutch energy firms – Eneco, Essent and Vattenfall – on Wednesday as part of their investigation into pricing practices.

The ACM said at the start of February it would carry out additional research to examine how the energy firms set prices and offset costs. The agency said it had decided to take a ‘closer look’ at these three suppliers because more than half of all Dutch households have an energy contract with one of them.

Price comparison website Energievergelijk said in mid January that consumers could save hundreds of euros a year by switching to a cheaper supplier and that the big three are all in the top five offering the most expensive energy.

The ACM said earlier this month energy firms must be more transparent about the tariffs that they charge new customers. ‘Prices energy suppliers charge new customers are falling, but they vary considerably among suppliers,’ the agency said.

Swedish state owned Vattenfall, meanwhile, said on Wednesday it is slashing its prices for gas and electricity because wholesale prices have also fallen.