I'll be posting one of my sourdough bread recipes this month and thought it might be useful for you to know how to make a starter first of all as you'll need it for the bread recipe.
So, choose the flour you want to bake with and mix 10g fresh yeast (any Tesco or Sainsbury supermarket with an in-store bakery will be able to provide this, you just have to ask them for it) with 250 ml luke warm water until the yeast is fully dissolved.
Then add 150g of the flour (I usually use either spelt wholemeal or rye as this gives the bread a lovely texture and flavour - also rye flour is gluten-free) and mix well until it's one smooth mass.
Now transfer this into a bowl, cover it and leave to mature for up to 4 days at room temperature.
You will need to stir it a couple of times a day, I use a whisk as it'll get more air into the mixture, and will notice it developing an acidic smell, which I find pleasant, but not everyone would agree with me ;) and should develop bubbles/foam.
Not a lot of work as you can see, but some forward planning required.
Bread recipe to follow mid-month