Shrimp & Pasta Shells Salad

Ingredients for 8 portions:
For the dressing:
1 1/4 cups mayonnaise
2 tsp Dijon mustard
2 tsp ketchup
1/4 tsp Worcestershire sauce
1 lemon, juiced
1 tsp salt, or to taste
cayenne to taste
1/4 cup chopped fresh dill
The rest:
12-oz package pasta shells
1 pound bay shrimp, or other small cooked shrimp, drained well
1/2 cup small diced red bell pepper
3/4 cup diced celery
salt and pepper to taste