Try Ship Lane, a turning off the B1007 south of the A12 at Galleywood. It's the 2nd on the left (east) after the twin roundabouts over the A12.
I went there with a small group of people in 2013 to look at a rare plant in Temple Wood on the corner (no prizes for guessing what sort of plant). During the 15 or so minutes we were there, any number of dodgy-looking motors passed us, containing even dodgier-looking big Essex guys sporting gold earrings and eyeing us with suspicion, until eventually a really spivvy fellow walked up and demanded to know what we were up to.
We learnt that he had a car scrap yard up the road, which he not very convincingly claimed was private, and were there not about 10 of us I am sure we would have been bundled out of it, in spite of our insistence we were just harmless botanists.
P.S. Go there at your own risk, and it wasn't me that told you, right?