In a large mixing bowl whisk together ½ cup mayonnaise, 1 tablespoon ketchup, 1 tablespoon lemon juice, 1 teaspoon lemon zest, ½ teaspoon Worcestershire, ½ teaspoon Tabasco, ½ teaspoon Old Bay seasoning, ½ teaspoon kosher salt, and a few turns of cracked black pepper.
Drain and gently pick over 1 pound crab meat, discarding any bits of shell. Transfer crab meat to bowl with dressing.
Add ½ cup chopped celery and ¼ cup sliced scallions. Gently fold together using a rubber spatula until everything is evenly coated and combined. Season to taste with additional salt, pepper and lemon.
Cover and refrigerate for at least 30 minutes to allow flavors to meld (or up to 4 hours).
To serve as a dip: pile crab salad into a serving bowl. Sprinkle with additional Old Bay seasoning and, using a microplane, grate fresh horseradish generously over top of crab salad. Garnish with celery leaves. Serve with celery stalks and buttery crackers.
To serve as a salad sandwich: spoon crab salad into Bibb lettuce leaves or toasted hoagie rolls, sprinkle with Old Bay and, using a microplane, grate fresh horseradish generously over top.