I'm sorry but I'm about to tell you something that will shatter your memories and faith but...
the mystical lands in the episodes of T-Bag were all sets! I know you wouldn't have known from the realistic life-like scenery but there you go.
All of the T-Bag series and specials were filmed at the Teddington Studios (previously called the Thames studios, by the river Thames.) with most of the series being filmed in the smallest studio at 43ft by 32ft, the illustrious studio 3. For more info about Studio 3 itself click here.
Filming for a series took on average 12 different days, one for each episode and two to finish of filming.
The images below show a floorplan and a 3D plan of Studio 3.