Responding to Leishman in the House of Commons, the prime minister said there was “no plan at all to support the workers of Grangemouth” before he took office.

“Within weeks, and importantly, we announced a £100m deal for a growth deal and we’re jointly funding Project Willow to find a viable long-term future,” he said.

The Labour leader added: “I take it very seriously and we’ll do everything we can to make sure that viable long-term future is there for the workers, for their communities and all that rely on it.”

Petroineos intends to turn the refinery into a fuels import terminal, which would require about 100 staff.

Earlier this month it closed the last synthetic ethanol plant in the UK, also at Grangemouth.

Ineos said while workers directly employed at the plant would be redeployed at Grangemouth, the closure would lead to a net cut of 80 roles, with more than 500 jobs impacted indirectly.

Billionaire Ineos boss Sir Jim Ratcliffe has claimed chemical manufacturing in the UK is facing “extinction”.