I created my own landowners permission form. In the pre-deployment survey phase, I email the landowner the form and ask them to return it completed. I also carry spares with my onsite survey docs that I take with me, never needed them but always handy I guess. The form's pretty simple and that's intentional. I kept it simple because landowners aren't experts and can become easily confused if it isn't simple.
I use the following form fields:
Street address (or 6 figure grid reference if none)
Landowner name and address
Proposed date & time (I usually ask for permission for whole days, rather than tying myself down to a tight time range)
Task Details (Short Description of the task)
Task Flight Info (proposed flight paths, altitudes etc.)
Consent description (what are they actually agreeing to, basically permission to operate SUAV's from their land).
Consent Signature and date
Emergency contact details (my air observer has a dedicated mobile number that is used to communicate with ATC, emergency services, landowner etc.)