Hi, welcome to OpenStreetMap and many thanks for contributing to this project.

I would like to make a couple of suggestions which might further improve the mapping for pedestrian navigation:

1) For most sidewalks in central London should probably be tagged with surface=paving_stones - although the paving stones may be mode out of concrete, surface=concrete is generally used for a poured concrete surface. In this area, a concrete surface is generally used only for service roads and as a temporary measure during construction works.
https://wiki.openstreetmap.org/wiki/Tag:surface%3Dpaving_stones

2) When you add a kerb node, please avoid putting it on the main line of the sidewalk. From the wiki:
"Please do not add a barrier=kerb on a node joining the footways near the crossing (e.g. sidewalk footway joining with footway crossing the road). That would implicate that such kerbs block not only crossing the road, but also just using the sidewalk (i.e. without intending to cross the road), which is almost never the case - and which has a big implication for several classes of users (most notably, wheelchair users)."
https://wiki.openstreetmap.org/wiki/Tag:barrier%3Dkerb#On_a_node
