Opposition Leader Peter Dutton’s plan to build seven nuclear reactors would take too long to replace ageing coal generators, the chief executive of the Australian Energy Market Operator has warned, as he backed gas as the grid’s “ultimate backstop”.

“Even on the most optimistic outlook, nuclear power won’t be ready in time for the exit of Australia’s coal-fired power stations,” AEMO’s Daniel Westerman said on Tuesday. “The imperative to replace that retiring coal generation is with us now.”