(1) OED states that "to drop the ball" is a North American idiom (probably makes more sense in baseball than in cricket), while the Cambridge Dictionary does not mark it as such. I believe, the expression is generally understood in Britain and nowadays used as well (correct me if I am wrong). Nevertheless, what would be the closest truly British analogue?
(2) What is the most idiomatic way of saying that one person made a mistake while another person failed to correct or mitigate it? Would it be normal to say
He dropped the ball, but you have not picked it up!
as a reproach?