Heat the flour and butter in a large frying pan, mixing to make a roux. Keep cooking until it’s biscuity brown, stirring continuously. Add the stock, vinegar, Worcestershire sauce, honey, sugar, bay and pepper, then season with salt. Bring to the boil, bubble for 2-3 mins, then add the beans and cook for 10 mins more. Can be made 1-2 days ahead; store in the fridge and reheat before serving.