Energy giant SSE insisted it was battling "difficult" energy market conditions as it revealed a £115.4 million loss in its retail supply business just weeks after announcing a hike in household bills.
The group, which has more than nine million customers and is the UK's second largest generator of electricity, blamed the performance on rising costs of wholesale energy, environmental and social policies and distribution.
Its overall underlying group profits fell 11.7% to £354 million in the six months to September 30.
The first half loss in its retail supply arm compares with a £48.3 million operating profit a year earlier.
SSE was the first of the major suppliers to announce a tariff rise, saying last month that it would lift prices by an average of 8.2% from Friday.
More top news
Former Conservative cabinet minister Lord Mayhew has died aged 86, his family has said.
Today's showery weather to mostly die out during the evening, only for rain spreading eastwards from the morning.
Thousands of people have attended celebrations around the country to mark Armed Forces Day.