Richmond park, Kingston is mainly a national park with a network of specific tracks and roads cyclists which make for a really good xc training sesion. There are also some paths which prohibit cyclists form using, which would make for some excellent short dh, but there is a fence in the way so we cant use them.
There are a few really fast runs with some well placed roots peeking up to boost you nicely clear of danger, if you picked up enough speed. Just watch out for other people. A lot of amatures use the main paths for training and leisure on sunny days!
Road bike users may also find the area of some interest as there are well maintained roads and some challenging hills with a super fast finish!
There are cycle hire facilities in Richmond Park in the car park near Roehampton Gate from April-September.