There were hopes the factory would create thousands of Welsh jobs after the company said earlier this year that St Athan was its "preferred" location.
The company Ineos said its new 4x4 cars will be manufactured in France, ending hopes that a new plant in Bridgend could be built.
The chancellor said Britain's "economic emergency has only just begun" and the damage to the economy caused by the Covid-19 pandemic is likely to be "lasting".