Lock Bike

I saw and heard them coming down the hill towards Parndon Mill and guessed that they were going to round the mill and cross the Stort Navigation at Parndon Lock. As you can see the guy in my image spotted me. In the next frame he's covering his face. The rider behind him gave me the finger. The third dirt bike bloke had engine trouble. 

I don't suppose it is legal to ride here, someone came out of the mill and spoke to the third man. I wasn't scandalised, though I know that a public footpath is not the place to put a motocross machine through its paces. I love wildlife and the countryside and am petrolhead. I've driven cars and bikes off-road and loved it. The lad in my pic has a nice bike and the correct kit. His helmet is Arai, the same as my son's. I wonder if there's a local track where they can get their thrills?