I vaguely remember an article about this in one of the Magazines. I think the issue is around the scope of the cover offered. The key is that the policy covers both you and the person upon who's land you have been given permission to shoot. As the land owner they have a degree of liability in their own right.
I would suggest ringing the helpline on both schemes and getting a feel for what they are like, what they know and how they answer your questions.