Hi Ton, basic batter as used in the chippy.
About 200 - 250gm of plain or self-raising flour, plus some for dusting
Baking powder: 1½ tsp if using plain, ¾ tsp if using self-raising flour
Ice cold tap water or soda water or beer. Enough to make a stiffish pouring batter
Put some dry flour on a plate so you can dust the fish fillets before battering. It helps the liquid batter to stick to the fish.
Put the flour and baking powder in a big bowl and using a whisk beat some air into the dry mix, or you could sift the mix into the bowl through a sieve. Keep beating and add the water/beer in a steady stream until a good pouring consistency is formed. Put the batter aside whilst you prep the fish and make the chips or for at least thirty minutes.
Get the oil hot... a drop of the batter should sizzle back to the top straight away.
When all is ready give the batter one last stir. Pat the fish dry with a paper towel or cloth then place it the in the dry flour and turn till it is fully covered. Dip the fish in the batter and let some excess run off then carefully place it straight into the hot oil. Do each fillet separately so that the oil stays hot.
I tend to double dip when battering so that I get a good covering. Any batter left in the bowl can be used to make "scraps" (the best part of fish 'n chips).