Mr Miliband said pricing needs to be “fair, transparent and fully justifiable”.

The letter to business suppliers from Mr Miliband and Ofgem’s interim CEO Tim Jarvis calls for a “fair and supportive approach”, with transparent contracts.

The Government also confirmed plans to use the Energy Independence Bill to regulate energy brokers and price comparison websites.

The effective closure of the Strait of Hormuz, a vital shipping route for oil and gas, and attacks on infrastructure in the Gulf by Iran have pushed up global prices.

The benchmark Brent crude was quoted at 108.21 dollars a barrel at the close of trading in London on Wednesday, well above the 73.08 dollars recorded on February 27, before the US-Israeli strikes on Iran which triggered the conflict.

Mr Miliband said the Government is “fighting people’s corner during this war” in the Middle East, with households covered by the energy price cap and action against “price gouging in the fuel market”.

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He added: “Today we are also stepping up to help small businesses get a fair energy deal.

“I have written to business energy suppliers, setting the very clear expectation that small business energy customers must be treated fairly, including by the brokers, who many small businesses rely on to negotiate their energy contracts.

“Following the conflict in the Middle East, pricing needs to be fair, transparent and fully justifiable, reflecting genuine market conditions.

“To ensure we do not see unfair practices continuing, in the upcoming Energy Independence Bill we will be bringing in new regulation of third-party intermediaries, such as energy brokers and price comparison websites, as a further measure to protect small businesses from harmful practices like mis-selling and untransparent pricing.

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“Ofgem will regulate the market, holding the powers to make rules, monitor the market, carry out investigations, and take enforcement action where the rules aren’t complied with.”