EDF has most complaints in big six
EDF was the most complained about of the "big six" energy companies at the end of the last year, according to figures demanded by regulator Ofgem.
The energy giant received 8,072 complaints for each 100,000 customers in the final quarter of the year - more than double the 4,001 logged by rival Npower, which received the second most complaints.
Under new Ofgem rules, the big energy firms must publish quarterly complaints data on their websites, including information about how many complaints were received and how quickly grievances were dealt with.
Britain's biggest energy supplier, British Gas, said it received 2,285 complaints per 100,000 accounts, while EON posted 3,023, SSE 1,435 and Scottish Power 1,359.
In its last quarterly report in July, watchdog Consumer Focus found EDF was the most complained about of the energy giants after it was the only one of the six to see an increase in complaints last year.
Consumer Focus compiled ratings based on figures from the Citizens Advice Bureau, the ombudsman and its own information from case workers dealing with vulnerable people.
EON, Scottish Power and SSE, which were the only companies to provide figures for the previous quarter, all posted an increase in the number of complaints on the previous quarter, with numbers traditionally rising over the winter months.
Ofgem said it was encouraging the companies to provide details of what measures they were taking to improve their performance.
The data showed EDF and EON were the quickest in dealing with complaints, with both managing to resolve 92.3% of complaints by the end of the next working day.
The new rules come after British Gas and NPower were fined £2 million and £2.5 million respectively for not properly dealing with grievances in 2011.