rainham marshes would be the one, back in the day there used to be big rc clubs always over there, best thing to do Is ask your local parks face to face.
I did this with weald park and bedfords park, I even asked them to put it in writing and I run my 1/5ths and electrics at both parks, all I need to do is give them a hours notice in case local dog walkers complain when I'm there