My leaven is alive and well. I used it for the first time on day 5 of the process of stimulating fermentation and at that stage I also used dried yeast. A week of so later and I'm baking using only the leaven. The first loaf for this is pictured below. Lovely, isn't it?
Unfortunately once I cut into it I discovered a hole large enough for potholing. The flavour and texture were good but it wasn't very good for sandwiches...
The latest attempt is below and I think may still suffer from the cave effect though not quite as badly. I've googled the problem and come up with all sorts of explanations - poor loaf shaping, over proofed bread, uneven yeast distribution, baking on a hot tray. Nothing definitive of course and there seem to be as many people asking how to get bigger holes in their bread (though perhaps not Wookey Hole sized holes) as there are looking into how to get a more even texture.
So far what I have noticed is that the texture of the dough is much more silky when using the leaven. Also the oven spring is good (i.e. the amount the bread rises during baking) but the texture is a little uneven. Oh and the bread doesn't taste particularly "sour" which I think may be because I am refreshing/feeding my leaven daily. Meanwhile my leaven is bubbling away nicely and being fed daily on flour and water.