Our standard batter is made with real ale. The real ale we use does vary, but for a particularly good batter a best or strong bitter is usually preferable.
A standard batch of batter consists of:
1/2 pint of soda water
1/2 pint of bitter
a splash (approx 50ml) of malt vinegar
pinch of salt
Put the soda, bitter, vinegar and salt into a tub or bowl and gradually whisk in the flour until you have a thicker consistency, enough to cling to whatever item you are battering, but without being too gloopy. The exact thickness is down to taste. If you over-thicken the batter, you can always thin it down again with a little water.
I would recommend a dusting of flour on your piece of fish or other foodstuff before placing in the batter, and allowing the batter to run off before frying so that it is not too thickly coated. You will otherwise end up with very heavy and stodgy batter.
An alternative batter we use is gluten-free. Originally we made this using gluten-free plain flour but this made a very hard and anaemic looking batter. After a curry night, we had invested in a bag of gram flour (besan) which is used to make onion bhajis. This is lentil flour and is completely gluten free. It also carries much more flavour and colour than some alternatives.
To make gluten-free batter you need to cut out the bitter (due the presence of barley, and sometimes wheat), as well as the malt vinegar. It is made purely from soda water, a pinch of salt, and the gram flour. The method is the same as above.