In a large bowl combine the flour and salt. Add the suet, currants (or alternate dried fruit), sugar, lemon and orange zest.
Pour in the milk and mix to a moist dough. If needed add another tablespoon or two of milk.
With flour hands, shape into a log about 8 inches long. place the log on a large sheet of baking parchment. Wrap loosely and tie the ends, much like a Christmas cracker.
With the water in the bottom of the steamer boiling, add the wrapped pudding in the steamer basket, cover and steam for 90 minutes.
Check the water level in the steamer periodically and top up if needed.
Remove from the steamer and allow to cool slightly. Slice and serve with custard. (See Notes).
Notes
Custard is traditional but another favorite is to spread with butter and sprinkle a little turbinado sugar.