My son was saying "I want damper!", so I went and did that kind of stuff.

450g plain flour
1 tsp salt
1 tsp baking soda/sodium bicarbonate
1 cup water with 1 tbsp vinegar

Mix, knead, bake at 200C for 30 minutes, on a floured tray.

I would have used self-raising flour, except I didn't have enough. I would have used baking powder instead of soda+acid, but there was none. Bah! Soda is the Traditional Way, anyway.

Buttermilk is standard, rather than acidulated water. Just has to be an acidic liquid, to react with the soda. Beer should work well, since it's acidic. The original version of the Guinness bread way well have just used beer/ale for acidity, with soda. Carbonated beer and self-rising flour are just modern frills, but they probably help make it a bit fluffier.