Beef in Guinness

1 kg chuck beef, cut into biggish 3cm  cubes, flour with salt and pepper 2 large onions, thinly sliced 3 carrots peeled and sliced 2 sticks celery, diced 1 tsp sugar 1 tsp english mustard powder 400 g tin chopped tomatoes 1 tblsp worcestershire sauce a bouquet garni 500 ml guinness salt and pepper to …