Pre-heat oven to 350 degrees Fahrenheit and grease an oven proof dish. Heat the oil in a pan and cook the pancetta until brown, then remove and drain on kitchen towel. Add the garlic to the fat in the pan and cook until lightly golden brown. Whisk in the flour and cook for 2 minutes. Whisk in the hot milk, for around 4 minutes until thickened. Whisk in the eggs until incorporated and cook for 2 minutes Remove from the heat and whisk in the thyme, cayenne pepper and the cheeses until the mixture has melted. If the mixture appears too thick, add additional warm milk. Place the macaroni in a large bowl, stir in the cheese mixture, add the pancetta and parsley, and stir until combined. Lightly stir in the crushed potato chips or crisps and stir in Transfer to the baking dish. Add some more grated cheese to the surface. Bake for ten to fifteen minutes, or until surface is golden brown.