Revealing mistake: When Flash says "I've got a plan and it's as hot as my pants", his moustache is seen falling off.
Revealing mistake: It is apparent that the door Flash pushes Percy through is fake. The door bends inwards like polystyrene when it should be made out of wood.
Answer: His first name is "Sod Off". Blackadder asks him in series 3 where this came from, and he replies "Well, when I was a kid, living in the gutter, I'd go up to the other kids and say 'Hello, I'm Baldrick'. And they'd say, 'Yes, we know. Sod off, Baldrick.'"
Shay