Apparently Catherine was having lunch with the African actor in the studio cafeteria before shooting and they got his order wrong. That's where the "this is not my sandwich" came from. She threw it in without telling him to try and get him to "corpse" (laugh)?
I was a set decorator for Catherine's shows. I can tell you that every single player here was 100% not offended. The African guy kept laughing and setting everyone off including the camera men and the production crew. The Chinese Lady was lovely and spoke perfect English.
It's from her show, The Catherine Tate Show. I think this was one of her regular characters in the show who, whenever a situation came up when they needed a specialist, she'd pipe up and say 'I can do it'.