From Bournemouth turn right onto the M25 to go past the Gatwick turning & towards Dartford. Just before you get to the Dartford crossing itself take junction 1A for Erith (A206). Go left at the top of the slip road onto the dual carriageway, over the next roundabout then right at the next into Joyce Green Lane. Follow this right to the end past lots of cows and the gun club, and watch for the signs by a gate saying go right here (or you'll end up in the Thames!).