Want to start buildering but afraid of being seen.

Hello builderers, first post here.

I recently started visiting a climbing gym and I’m a pretty decent climber (I think :P), and I would very much like to get into some buildering. There are a few things to climb in my area, but I live in a fairly small English town, but can get to larger places fairly easily. If any of you are familiar with the area, I live near Middlesbrough, on the coast.
However, my big problem is that I am afraid of being seen by anyone. I’ve found it very difficult to find any information at all on this kind of thing and the legality of buildering, and where I would builder, I think I would almost always be seen. Can anyone give any advice on this? Do you avoid other people, go after dark, or do they tend to just ignore you?

Thanks in advance.

P.S. How sturdy are plastic drainpipes? 😛