Just back from hols to read about this. Absolute shocker. Yes, the landowner should be taken to court and the maximum possible fine applied. Even if it was a contractor who actually "did the deed", the landowner is responsible for ensuring the contractor knows what's what. Besides which, ignorance of the law is no defence.
EH need to act now and publicly. Actually, shouldn't it be the police stepping in, as damaging a scheduled moument is a criminal rather than civil matter. Otherwise the message that this sends out to other landowners with troublesome scheduled monuments on their land is pretty clear, isn't it?