Engineering Diamonds

My uncle and grandpa used to work at Engineering Diamonds when it was based in Warwick Row. Mum has been trying to remember where it was exactly and has a memory that it was in a cellar and somewhere near the Pepper Pot Cafe. If you looked down through a window, you could see the men working at the diamond cutting.
as a child, I used to think of them cutting big sparly diamonds for jewellery until grandpa told me that it was for cutting tools, I was very disappointed after that as it seemed so boring and ordinary.
Anyway, can anyone shed any light on the exact whereabouts of this workshop and when they moved?
as a child, I used to think of them cutting big sparly diamonds for jewellery until grandpa told me that it was for cutting tools, I was very disappointed after that as it seemed so boring and ordinary.
Anyway, can anyone shed any light on the exact whereabouts of this workshop and when they moved?