Claims that power plants are gaming the system to charge huge sums to switch on in the UK’s cold weather

• No 10 insists UK has sufficient energy supply

A rise in electricity costs this week has raised fears that officials operating Great Britain’s power market could be held to “ransom” by owners of gas power plants during cold, windless days in order to keep the lights on. Here, we look why costs have increased sharply, the trading rules for plants and the implications for Labour’s clean power ambitions.