Melt the butter in a saucepan, and stir in the flour to make a roux.
Add the mustard, cayenne pepper, salt and pepper to taste.
Stir in the ale or beer until the sauce begins to thicken, then add the cream as you continue to stir.
At this point, you will want to make the toast.
Add the cheddar and stir as it melts into the sauce, making it smooth and creamy.
Add the Worcestershire sauce and lemon juice last, continuing to stir at a fairly quick pace.
Once the mixture is thoroughly blended, remove from the heat immediately.
Arrange the slices of toast in a shallow baking dish. Divide the cheesy mixture between them, spreading over each piece to cover the surface.
Place under the broiler for about 1 minute until it begins to bubble.
Sprinkle with parsley and serve immediately.