The Conservatives are threatening a review of Channel 4’s broadcasting remit following a row that saw a melting block of ice stand in for Boris Johnson during a climate change debate.

The prime minister was branded “a coward and a bully” by Labour after the Tories complained to Ofcom about Thursday night’s debate and accused the broadcaster of “conspiring with Jeremy Corbyn”.

Mr Johnson refused to take part in Channel 4’s debate, and the broadcaster refused to accept his underling Michael Gove as a stand-in, stating that Mr Gove was “not the party leader”.

In place of the prime minister, Ben de Pear, editor of Channel 4 News, said the broadcaster would put “two ice sculptures [that] represent the emergency on planet Earth”.

He said the melting ice was a “visual metaphor” for the missing leader, as well as Nigel Farage, who also declined to take part.

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An angry Tory spokesperson said: “We are deeply disappointed that Channel 4 News has conspired with Jeremy Corbyn to block the Conservatives from making the case for tackling climate change and protecting the environment in this evening’s debate.

“Under this government the UK was the first advanced economy in the world to legislate for a net zero target and we’ve reduced emissions faster than any other advanced economy while continuing to grow our economy.

“Broadcasters have important responsibilities to present a balanced debate representing all parties, and Michael Gove was well qualified to represent the Conservative position at this evening’s debate.”

But Labour MP Clive Lewis said: “Boris Johnson is a coward and a bully. He thinks he is born to rule and is so used to getting his own way that he turns nasty when anyone dares challenge him.

Jeremy Corbyn, Sian Berry, and the ice block (Channel 4)

“Britain deserves a prime minister that has enough of a backbone to face up to scrutiny.”

During the relatively good-natured debate, the leaders from the other parties put forward their climate policies. Jeremy Corbyn said the election was the last opportunity to address the climate crisis, Jo Swinson said Brexit would make the situation worse, and Sian Berry of the Greens said the other parties were doing their best to sound like hers.

In a letter to Ofcom the Conservatives said Channel 4’s policy “effectively seeks to deprive the Conservative Party of any representation and attendance at the Channel 4 News debate”.

The explicit threat to review Channel 4’s remit was made by a Tory source reported by the BuzzFeed News website – and was not made on the record.

It was also pointed out by some on social media that the letter misspelled the word “judgment” and was therefore unlikely to be a serious threat as it would not have been written by a lawyer.

Labour’s deputy leader Tom Watson last night wrote to Ofcom’s chief executive Sharon White, urging her to “call out this meddling”, adding: “We need a strong free press. But the Tories are restricting journalists. This campaign, Boris Johnson has banned the Daily Mirror from its battle bus, ducked the Andrew Neil interview and now attempted to bully Channel 4.