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"Every start and switch-off of the engine counts as one cycle," he explained.

The switch-off will begin on a smaller scale, and affected homes and businesses will be contacted by suppliers "well ahead of time", the energy department said.

Fuel poverty campaigners said the switch-off process had been "doomed to failure" after it became clear that the 30 June deadline was "simply unachievable".

He called for a plan "that sets out how the gradual switch-off will take place, including which regions will be affected and when".

RTS meters typically control heating and hot water on a separate circuit to the rest of the household's electricity, so things like plug sockets and lights are unlikely to be affected by the switch-off, Ofgem said.