Combine steak, kidney, onion, celery salt, pepper, salt, and thyme in a large bowl.
Sift flour and salt into a bowl, then mix in suet, pepper, and water gradually.
Cut through the dough using a round-bladed knife to reach the correct consistency.
Mix with your hands to form a soft dough.
Roll pastry on a floured surface to 1cm thickness and cut out a quarter for the lid.
Line a buttered 1.75l pudding basin with the remaining pastry, leaving a 1cm overhang.
Coat the meat mixture in flour and sieve to remove any excess.
Spoon meat into the basin and pour in beef stock until two-thirds full.
Place the pastry lid on top and seal the edges securely.
Cover with pleated buttered foil and tie tightly with string.
Steam the pudding in a saucepan of hot water for 5 hours.
Turn the pudding out onto a warm plate and serve with mashed potatoes and peas.