A statement issued by the watchdog said: “Broadcasters have editorial freedom in determining the format of any election debate. Depending on the circumstances, they may choose to proceed without having agreed the participation of a particular political party or politician, providing they take steps to ensure the programme complies with our due impartiality and elections rules.
“In this case, the Election Committee concluded that, across the one-hour debate and a subsequent news programme, Channel 4’s use of editorial techniques ensured that the Conservative’s viewpoint on climate and environmental issues was adequately reflected and given due weight.
“The Committee also took into account that the globe ice sculpture was not a representation of the Prime Minister personally, and little editorial focus was given to it, either visually or in references made by the presenter or debate participants.
“The Committee therefore considered that this programme, including the use of the ice sculpture, did not raise issues warranting further investigation under our due impartiality and elections rules.”