Our 7 was manufactured in the Norwich factory where Elises are done nowadays. However, many (most?) Sevens were produced in the Cheshunt factory in the Great London Area.
A visit September 2008 confirmed that the old Lotus buildings are still there. The Lotus main building is now a plastics factory and the building where Lotus Components resided is now a fitness center. The buildings as such seem unaltered, even the winch where they lowered the Sevens from the first floor remains, as does the ramp of the Lotus factory.