Stir together first 5 ingredients.
Place shrimp in a large Dutch oven; pour Worcestershire sauce mixture over shrimp. Squeeze lemons over shrimp mixture; add squeezed lemon halves and 1/4 cup water. Bring to a boil over high heat, stirring frequently; cook, uncovered, 6 minutes or just until shrimp turn pink, stirring frequently. Remove from heat.
Gradually add butter, stirring until butter melts. Serve immediately with crusty French bread.