In reply to Roobag:
Most of the stuff in Essex is somewhat dodgy climbing / bouldering on man made structures - particularly railway bridges.
The only place of note (and I appreciate it's a long way from your part of Essex) is the artificial boulder park at
Fairlop Boulders ; with boulder problems (or in some cases easy short top-ropable problems) up to V3 / 6a. See
http://www.rockworks.co.uk/UserFiles/file/Fairlop%20Waters%20Climbing%20Gui...
There are a few other artificial boulders dotted around the 'inside the 25' part of Essex, but they are prone to vandalism / fires whilst Fairlop is usually very clean.