Finally, I've successfully produced a stable and reliable sourdough starter. The starter has been bubbling away for about 3 weeks. To begin with, I fed her as per the method in the book I'm using: Do Sourdough. There are a couple of sourdough bread makers at work and one of them recommended keeping the starter going with equal amounts of the starter, new flour and water.
Since 29th February, I have been discarding half of the starter and refreshing it with 50g of organic wholemeal flour and roughly 30-50ml of water depending on the starter hydration - you don't want it too wet. To avoid issues with chlorine, I let the water rest overnight in a jug, although on one day I did use water fresh from the tap. Apparently, the natural yeasts can overcome the chlorine but in the early days of the starter, it is best to use spring water.
The starter has been living in the airing cupboard. I tried a day outside of the airing cupboard, but she's happier in there. This morning I took 150g of the starter, added 120ml of water at 35°C to break it up and then added 100g of white and wholemeal flour to make the production sourdough starter. This is the first step towards bread. I will know in 4 hours or so if this has worked.
I've fed the starter today but I suspect she'll go in the fridge tomorrow. I'm experimenting and I'm not sure I'm going to bake every week - I only eat carbs on cheat day. But if you are going to have bread, you may as well have good quality bread.