Hob,
The cave at the Langdale axe factory appears to be man made, and is well worth a visit. I have never been able to find anything out about it. It's got a roughly rectangular entrance. There's room for, as I recall, about 6 people in comfort, and is rectangular inside. It's about 1800 feet up. If you were descending the scree gully it's on the right hand side, in the rock wall. Obviously, I like to think the old people hacked it out in order to shelter there whilst axe making. It looks too much of a regular shape to be natural, but it must have taken some making. I always fancied a night there, but never got round to it, as the Yates bitter at the ODG kept calling me.
In years past we've descended down the scree slope, after a days rock climbing, at frightening speed, like riding a wave of loose stones, but erosion has resulted in a request not to do it, so I stopped. All the stones are getting pushed further down towards the valley, leaving loose earth.
There's a book out about Great and Little Langdale valleys by Bill Birkett. I've only browsed it at Waterstones, but there is mention of other prehistoric sites in the valley. I didn't have enough time to digest it.
All the best,
TE