The downy birch and its sister tree the silver birch are both natives of Britain.  The birch is an easy tree to identify; no other tree has a bark so unique. However, the downy and the silver birches are very similar and it is difficult to distinguish between the two. They have similar bark, though the downy is usually whiter, less of the black bits; these are bad examples. The nuts (catkins) are similar, the leaves are similar, everything is similar. You have to get up close and feel them to tell the difference. Incidentally, though these downy birches are not great examples, they are worth looking at because the downy birch is a lot less common in London than the silver birch, and there aren't any silver birches in Lincoln's Inn. The downy has smooth, downy shoots; the silver birch has hairless and warty ones. Downy, in this context, means feathery or fluffy, hairy.