Downy ?

The quest to get certain identification of a downy birch that is not some kind of hybrid continues. So the Woodland Trust's guidance should help. Identification guides are always flawed to a degree and the best bet is a combination of several of them allied to plenty of direct observation.

The key features according to numerous sources include being more upright, having a more brown bark and more horizontal grooves. All things are comparative and how much is 'more'? Another association that's mentioned is the presence of 'Witch's Broom'.

The most notable Witch's Broom on Blacka is this one and this year it's grown even grander.  It's decorative in winter too when covered in snow. The same tree is showing good downy patches on the back of leaves.

But upright? This test it fails. It's almost supine in fact.