[kagamine]

Like everything in UK law it is interpretation (of a police officer and a judge and your defense) and any given circumstance. If you sleep in the back of a camper van with the key in the glove box and the doors locked a police officer would be hard pushed to convict you of attempting to drive. Don't freak out just yet. Now go out of the vehicle and stand still for a while on a dark night. You are now loitering with intent (to burglarize perhaps). Now put a reflective jacket on over your dark hoodie; you are now absolved of suspicion. Get back in the camper van and have a peaceful 40. Just about anything is illegal with the wrong attitude. In the UK, my experience has been to just talk to the police and be honest, they're usually quite smart.