The Office of Fair Trading has announced it will examine the market for off-grid energy consumers following increasing public concern.
The study would look at whether the market was working for consumers who were not connected to the main gas grid and used energy sources such as heating oil, LPG and renewable sources like solar panels.
The OFT said it had brought forward the investigation following discussions with the Department of Energy and Climate Change (DECC) to allow time to consider any recommendations before next winter and in light of increasing public concern about areas of the market.
The OFT wanted the study to cover the whole of the UK and look into how well competition was working for consumers and whether they were given clear information, competitive prices and fair terms and conditions.
It also planed to survey off-grid energy users around the UK.
OFT senior director of infrastructure Heather Clayton said two and a half million people relied on off-grid energy and it was vital the markets that supplied them functioned as well as they possibly could.
"We will be taking both competition and consumer issues into account through this comprehensive look at the market."
The OFT said it would work with other bodies such as Ofgem, the Scottish Government, the Welsh Assembly Government, the Northern Ireland Executive and Trading Standards.
It expected to conclude the study in autumn of this year.
The OFT had already announced it was monitoring prices of suppliers.
More than 1.5 million homes were dependent on oil and 150,000 needed deliveries of liquefied petroleum gas for their heating, cooking and hot water.
Energy minister Charles Hendry said many off-grid energy consumers had been hit hard by high prices and supply issues this winter and he was keen that the reasons for this were “thoroughly investigated”.