Are you sure? I've been told I need to take it into them?
I've never had to show my copy of a DBS or CRB to any of my employers when they've ran the check. They may want to see your copy just in case they don't get theirs before you, but they get a copy of it and can check online as well. Just explain to them that it has been damaged in the post when you take it in to them. If they're reasonable they'll be cool with it.