Three British energy companies - Green Energy UK, Avro Energy and Green Supplier - filed for bankruptcy on Wednesday.
As a result, 800,000 Britons lose their supplier.
High energy prices are the main cause of the financial problems, it is said.
Together, the companies controlled about 5 percent of the British energy market.
It is not yet clear where the customers can go.
Green Energy pointed in a short statement to the "failure of the government, which did not support small energy companies".
The company refers to the energy crisis on the European market, resulting in large price increases.
Prices for gas and electricity have risen rapidly in recent months.
Price comparator Pricewise calculated on Friday that an average Dutch household spent 500 euros more in energy in the first half of this year than a year earlier.
Green attributes the sharp price increase to a number of factors, including Brexit, the blockade of the Suez Canal by the freighter Ever Given and a fire in a pipeline between the UK and mainland Europe.
The British regulator Ofgem warned on Wednesday that even more energy companies will go bankrupt in the coming days.
Keywords: