Isn't the solution to have legal insurance - covers the worry of having to defend a claim, usually a small add-on to household insurance - c£25? I am not aware that it restricts in what capacity it arises but worth asking.
Also my household insurance cover's my farm buildings as well as my house therefore I have public liability cover that way. Doesn't cover stray sheep (or loss of farm implements, but we take a self-insure approach to these) but helps if someone walks into the tractor or trips over a harrow.
However... do all
businesses have to carry Public Liability insurance? Got me wondering.....