I have only seen the Broadway production on video (which is not quite the same) but IMO the London staging was far superior - if you could have mixed the cast up a little and then used the Phoenix production it would have been stunning.
The set was a vast curved wall filling the stage from each side of the pros to the rear in a semi-circle with lots (nine or more?) of arched double doors set into it, with a design of branches above the doors and a vast clock at the rear. The doors could be opened mechanically. Julia McKenzie (as the witch dressed in black, hooked-nose, warts and all) ate the items collected by the baker, started to convulse, and then ran screaming through the downstage door on the left, around the semi circle seen by the audience as she passed each open door. There was a small puff of smoke as she entered the left door which blurred rather than obscured her and as she reached the downstage right doors she cast off the black cloak and emerged through another small puff dolled-up to the nines, bejewelled and dressed in white. I saw the production three times and each time this got an enthusiastic round of applause.
In truth this was a very simple deception, but done so well that jaws hit the floor. Kovari was the consultant for the magic and certainly delivered the goods - no other production (that I have seen) has lived up to the sparkle that the original London production had, and some (yes Kerryson I am talking of your limp Leicester version) have failed miserably.