Fold whipped topping into chocolate sauce just until blended.
Split cake horizontally into three layers.
Place one layer on a serving plate.
Spread with 1/4 of the topping mixture and 1/4 of the toffee bits.
Repeat layers.
Frost top and sides with remaining topping mixture.
Sprinkle with remaining toffee bits.
Cover and refrigerate for 4 hours.
Store in the refrigerator.