Civil ceremony?

Well to start with in England and Wales you can't get married outside (unless in a gazebo or some sort of permanent structure). I'm also fairly sure that to have the legally binding religious ceremony it would need to be in a church.

What you could do is do the legal bit at a registry office then have a religious blessing in a forest and see that as the 'real' ceremony. If your priest / vicar / rabbi (what religion are you by the way?) was up for doing that.

Humanism is a 'religion' of its own and not a term to describe outside weddings. Humanist ceremonies aren't legally binding in E&W - they are in Scotland though.