I found some sand, but a bit different to that of the video!. There's a green lane near Dorking, starting from the A25 near Wotton, it starts as a lane called Wolvens Ln and carries on after that, Google map
here.
They seem to maintain the trail by filling it with sand to cover the ruts. I was lucky not to drop the bike a few times, the front wheel was everywhere. The trail is popular with hikers and cyclist as well so going quick is not always possible, so those patches of sand became really tricky. I used to compete in Downhill and Mountain bike races back home so maybe that makes up a little bit for my lack of motorbike riding experience and skills (my first bike...). I am looking for a group to go out with so I can learn quicker and better.
Someone said in this thread that cleaning the bike wouldn't be fun, it's not!. I had sand even underneath the seat!
I hope someone can enjoy that green lane too.
Cheers.