Liz Truss has failed to guarantee there won't be blackouts this winter as fears mount over energy supplies.
The Prime Minister ruled out energy rationing during the Tory leadership contest and Downing Street insisted in August that Brits didn't need to cut their usage.
But the National Grid said today that there could be rolling three-hour planned power cuts in the "unlikely" scenario that supplies run extremely low.
The PM was grilled on the grim warning on a visit to Prague where she urged European leaders to help "keep the lights on" this winter.
Asked what she would do to prevent blackouts, Ms Truss said: "We're working very hard on energy security, it's one of the reasons I'm in Prague today.
"We have interconnectors with our European partners, we're working on more gas supplies, we're working on building out nuclear energy, building out wind energy, so we do have a secure supply."
Pressed to guarantee there wouldn't be blackouts, she said: "Well what we're clear about is we do have a good supply of energy in the UK, we're in a much better position than many other countries.
"But of course there's always more we can do."
Told it sounded like she was backing off the guarantee, she said: "What I'm saying is we do have energy supplies in the UK, we can get through the winter.
"But of course I'm always looking at ways that we can improve the price for consumers. That's why I put in place the energy price guarantee, as well as making sure that we have as much supply as possible."
Households are being encouraged to "save money and back Britain" by using more energy during off-peak times.
The threat of rolling blackouts was presented as the worst-case scenario in a report by the National Grid Electricity System Operator (ESO).
It still expects energy demand and supply to be sufficient to cover households this winter.
Planned blackouts hit the UK during the 1970s in response to the miners' strikes and the oil crisis.
