Heat oil up in a deep pan or automatic deep fat fryer to approximately 375 degrees F (or a fry setting, if your fryer has one).
Peel the potatoes and cut into chunky sized chips. Rinse and dry thoroughly.
Fry chips for about 3 minutes until soft but NOT coloured. Drain and shake well and set to one side.
Put some flour onto a plate. Dredge the fish fillets in the flour thoroughly - this is VERY important, it stops the batter sliding off when fried! Leave the fish fillets in the flour whilst you make the batter.
Put flour, bicarbonate of soda, salt and pepper into a large roomy bowl. Add the beer gradually, stop when you have a thick coating type of batter. Drink any beer that is left! Whisk thoroughly until it is smooth and there are no lumps. Add the lemon juice OR a splash of malt vinegar, if desired. Mix thoroughly again.
Have your plates, newspaper or whatever ready for eating!
Adjust deep fat fryer to fish frying temperature of approximately 325 degrees F (or a fish setting, if your fryer has one).
Take one fillet of fish at a time and holding it by the tail or thin end (!) swirl it around the batter until well coated - plunge into hot fat immediately. As soon as it has crisped up and set, add your other fillets one at a time, taking out the first ones as they cook - about 6 to 10 minutes depending on the thickness. Place onto a wire rack in a baking sheet with sides and keep warm in the oven.
Turn up the heat setting again to 375 degrees F and cook your chips until golden and crisp.
Serve on plates or newspaper with salt & vinegar!