While she is only a tenant farmer her landlord is also happy for me to shoot these vermin. The information that I have managed to gather so far leads me to believe that all I require is written permission to shoot on said land. Is my information correct?

Shooting legal advice
The shooting of pest species is controlled by general licence. Shooting crows that are attacking sheep is covered by the licence.

You should read the licences, which can be viewed at www.basc.org.uk/content/pestandpredatorcontrol, before you go shooting.

Note that different parts of the UK have different licences and that they are reviewed from time to time. I recommend that you check early each year to see if any changes have been made.

Your tenant farmer is an occupier for the purposes of the general licensing system and may grant authority to ‘authorised persons’ to carry out pest control on her behalf.

It is helpful, but not essential, if the permission is given in writing rather than orally.