Not sure I look the like of Mote End, had a quick look with a friend and it looks more like a construction plant hire site and with shipping containers all over the place
Would you be able to get out to Berkshire area? A friend of mine lives in SW London and has her dressage horses down the M40 at a lovely dressage yard; it's near the Chiltern Equine Vets but I can't remember the name of it; there must be other good yards in the area though as it's on the way to Bury Farm. I think she goes three evenings a week after work and at the weekends, it takes her about 40 mins if there isn't any traffic.
Wild Farm in Radlett. Owner is a Grand Prix rider. Lovely listed courtyard, long arena, post and rail individual turnout and off road hacking. 07590 058954