IBC Vehicles' plant in Luton, which builds the Renault Trafic and Vauxhall Vivano, went to three-shift working during May.
The move allowed the transfer of more than 1,000 workers from the neighbouring Vectra car assembly plant, due to close next March.
Nick Reilly, chairman and managing director of Vauxhall Motors, said: “It means there have been no forced redundancies at Luton and things are back to normal for us. “This is an important landmark for the plant and shows our commitment to van production in Luton which was part of our long-term manufacturing plan.”
The expansion at IBC takes the total workforce to 2,800 - more than twice the number that worked there when IBC Vehicles was formed in 1987.
The integration of Vauxhall employees is said to have worked well. Current production is 300-400 vans a week, working up to full production of 1,834 a week.
The plant benefited from investment of more than £130m, shared between Vauxhall, Opel and Renault, partners in the X83 van project.
The investment has more than trebled production capacity. Last year, IBC built 35,000 Fronteras. Production of the 4x4 was halted during the redevelopment and will start again this summer alongside the van. About 8,600 Fronteras will be built this year rising to more than 16,000 next year.