Preheat the oven to 220˚C/200˚C fan/gas mark 7. Spread 1 x 180g bag of tortilla chips on a large rimmed baking tray. In a saucepan, combine 350ml Buffalo wing sauce with 100ml water. Place over a medium-high heat and bring to a simmer. Add 500g shredded cooked chicken and cook for 4-5 minutes until completely heated through. Remove the chicken using a slotted spoon, reserving the sauce, and spread evenly over the tortilla chips. Top with 200g grated Cheddar. Bake in the top half of the oven for 5-6 minutes until the cheese is melted. Scatter over 120g crumbled blue cheese and 2 chopped celery stalks or 2 chopped spring onions. Drizzle over the reserved sauce and serve.