To add somewhat to what Tim is saying, it appears you’re arguing for criminal trespass. That’s the good, meaty one that will get some action, right? Also the hardest to prove. As with most criminal acts, there is an essential element of intent. The person had to reasonably know they were trespassing, or it’s at best negligent (and you’re straying into tortious trespass which is a civil action).
You see, as a tradesperson with instructions to work on the site there‘s almost no chance you’re going to be able to prove they were intentionally trespassing. In their minds, they thought they were invited in to do the work. And, really, even if you could cobble some credible evidence together, you’re going to have to convince the police to do something about it. Let me tell you, they let bigger transgressions walk away due to lack of interest/too hard/not ‘sexy’ enough/too close to a civil matter and just don’t want to get involved.