This wall is situated inside the Seymour Leisure Centre (social sports centre owned by Westminster City Council) and as such it's rather low-key, maybe off-putting...
... but it actually is one of the best indoor climbing places in London!
It's very central (Baker Street / Edgware Road / Marble Arch stations), open late during the week, and quite cheap (£8 for registered climbers or £4.5 if you have an address in Westminster - work will do if you live elsewhere, just ask for the free resident card) and very nicely designed.
West 1 is quite small but they have dug through the lower ground floor and the cellar so that the routes are 13-meter high. That's as high as the highest routes at Westway or the Castle. There are 12 ropes, or ca. 35 routes, which is not much but the staff and route-setters have done their homework and know their customers well...
There are four ropes for absolute beginners (4 to 5+ on a vertical wall and a slab) and height other ropes for more seasoned climbers; these routes range from 5 to 7b (a couple each at both ends of the range). If you want easier routes, you just use the other ones (and don't jam the place for others), and no room is lost to ultimate grades (that's 7c and above, to me, and if you're that strong you probably should be outdoors :-)
Conclusion : you can come here for three hours and not get bored.
And there is a bouldering "cave". Some of the problems are for beginners (so that kids sessions don't monopolise the wall), the others for x-men (up to V10 - if you wish there were 8a routes on the wall, for example).
Finally the centre is very clean (chalk vacuumed regularly), not well known and quiet (we had it just for ourselves several times this summer - but if more people don't come, it's going to become an issue) and the route setters are good ones (Mike the incumbent, not boring at all, Gaz Parry and Yann Genoux - Gaz being the big strong guy and Yann the clever tricky one).
Do give it a try, maybe check their Facebook page first (they also have a website but their FB photos are better). read more