In a small bowl, combine the ketchup with the horseradish, Worcestershire sauce, Tabasco and lemon juice. Set the cocktail sauce aside at room temperature.
In a large bowl, combine the back-fin crabmeat with the cream cheese, sour cream and 1 tablespoon of the chives. Spread a 1/2-inch-thick layer of the crab mixture across a large platter and top with the cocktail sauce. Scatter the lump crabmeat on top and garnish with the remaining 1 tablespoon of chives. Refrigerate the crab cocktail until slightly chilled. Serve with cucumber slices, crackers or toasts.
The crab cocktail can be refrigerated overnight. Remove the cocktail from the refrigerator 15 minutes before serving.