Preheat the oven to 400 degrees. Thaw the puff pastry according to package directions. Combine the broth, potatoes, carrots and celery into a Dutch oven or large, heavy pot, and bring to boil. Reduce the heat and simmer 25 to 30 minutes or until the vegetables are tender. Meanwhile, cut the pastry into 8 squares and bake on baking sheet until golden brown, 10 to 13 minutes. Add the chicken to the vegetable-broth mixture and simmer 10 to 15 minutes. Stir in the onion and peas and simmer until heated through.
In a separate saucepan, melt the butter and stir in the flour. Cook, stirring constantly until almost golden. Add the cream and bring almost to the boil. Reduce the heat and simmer 2 minutes. Add the lemon juice and Worcestershire, and season with salt and pepper. Add this mixture to the chicken mixture. To serve, ladle into bowls and top with a puff pastry square.