The widespread cutbacks will cover Opel/Vauxhall, Saab and its partnership with Fiat, says the Daily Telegraph today.
Fritz Henderson, GM Europe chairman, said yesterday: "Revenue generating capacity is way short of what we assumed.
"Our assumptions on volume and market share were wrong and picking up market share in Europe is incredibly difficult."
The company has just announced that its Korean Daewoo name will be subsumed into the Chevrolet marque across Europe as its low-cost value brand. While it expects the Chevrolet name to double Daewoo sales next year and take 2pc of the European market, it admits that the Opel/Vauxhall names are in trouble.
Henderson is touring his plants at present and intends to make a decision some time before December.
"I need to have a significant impact in 2005," he said, "so I need to have a plan in place in the next 60 days - we don't have the luxury of time."
The most likely victims of the cuts will be the Saab plant in Trollhatten.
Britain appears to be relatively safe from the proposed cuts as the Ellesmere Port plant is making the highly popular Astra five-door and its V6 petrol engine making wing was closed this June.