Oh dear!!! I'm not sure how you stand with this one, but it might help if someone else's also seen, or had rats, and then you could complain together. If it was me, i think I'd make a writen complaint to the head of the department, saying that you aren't satisfied with the answer you've been given. If permission's needed to access the private land - which it probably is - then the EH can SEE that they need to have a word with the owner. I'd also point out the very real possibility of catching Weil's Disease, and see what they have to say. x