GY Equine have just taken a small yard on to the north of Braintree, she offers full livery and the option of schooling (she schools mine) pm me if you want the info?
I think you need to be more specific about what you mean by exercise. If you mean hack/ride a couple of times a week or have a pro school it on. There are plenty of pros around Essex depending on if you are looking for SJ/eventing or dressage emphasis. It's going to be pretty expensive though I should think around £160 pw+ and the grooms might actually do most of the exercising.
CBAnglo good point I should of been more clear. I am coming back into riding after injury and need him school be it hacking or in the school by somebody who will keep him working along nicely so when I get on it hasn't fallen apart between rides. My riding had also go backwards a lot so I need somebody experience to help him learn.