Controversial plans by the competition watchdog to let energy companies access the contact details of millions of households who have not switched supplier have come under fresh attack from the data protection watchdog.

The Information Commissioner has warned that it has major concerns over the plan by the Competition and Markets Authority (CMA) for a new database to let energy suppliers send marketing mail to customers of rival firms.

The move was an “intrusion on individuals’ privacy”, it said.

The proposal was one of the CMA’s flagship ideas to improve competition in the energy sector after a two-year inquiry that concluded households were paying hundreds of pounds a year too much for their gas and electricity by not switching.