Martin Lewis has warned energy bill prices could rise to £2,900 a year if prices continue to surge at the current rate.
The Money Saving Expert appeared on This Morning to issue advice to viewers.
A caller contacted ITV's flagship daytime programme to ask the finance guru whether she should opt for the fixed or variable rate on her energy bills.
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The price of energy bills will skyrocket when the price cap rises by 54% next month due to the surging cost of wholesale gas.
Martin's advice throughout the crisis has been to stick with the price cap as this has represented a more cost-effective deal than any fixed contract.
However, the price cap is based on wholesale rates that energy firms pay over six months.
Russia's invasion of Ukraine prompted the price of wholesale gas to soar to record highs this week - and Martin warned bills could surge again in October.
He said: "We are one month through that six months now so it's a lot of crystal ball gazing right now and I cannot promise my answer I'm going to give you now is correct, it's just my best guess.
"But based on where we are currently, after the hideous things having gone on in Ukraine, which means wholesale rates have spiked.
"It's looking like in October, on top of the 54 per cent rise in April, we will see another rise of around 45 to 50 per cent, taking a typical energy bill to £2,900 a year.
"Clearly, we will need intervention on that and more than what we have had at the moment."
Martin said the situation is still unknown, but advised people to opt for a fixed deal no more than 25 per cent above the price cap if they wanted certainty.
He said: "If you look on it just on that basis, and that's only one month into the sixth month assessment period, it could get worse and it could get better.
"But based on that right now, if you can find a fixed deal for a year or longer that is no more than 25 per cent above the April price cap, then I would look at fixing if you want price certainty.
"I can't promise it'll be the best outcome. If not, I would stay where you are and stay on the current price cap."
Martin branded the uncertainty around the situation as "horrendous" after he issued the advice.
He said: "I've never had anything like this before. Energy used to be giving people a standard answer of what's cheaper. Now it's doing risk analysis. It's horrendous."
This Morning airs weekdays at 10am on ITV and ITV Hub.
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