The dished plates both need to have the dish going toward the center of the stack.
Warped steel plates is the most common cause of this sympton. Take out all the steel plates and lay them flat on a piece of glass or other known perfect flat surface, and check them for flat. If any are not flat, replace them.
When the clutch pressure is released, there is just a little bit of room for it to spin free. Even small amounts of plate warpage will cause drag, and then they make heat and warp even worse. The plates need to be flat, and they very often are not. Even check the brand new plates, because they sometimes come warped from the factory.
Also, never hold the clutch lever in at stop lights or or anything. Use neutral, and just pull the clutch lever in when you need to put it in gear. Holding the clutch in will heat it up and possibly warp the plates, and also friction-weld the steel ball to the steel rod in the throw-out assembly.
A lot of Brit bikes have these same clutch issues. It's not just Enfield.