I occasionally need to use my own car when a mil veh is unavailable. I understand that I now have to have business ins to cover me on these trips.

Any idea where I get this from ? I am with AXA (thru OGirke) and wonder if anyone has an idea of the increased premium cost ? If it costs an arm & a leg then I may travelling by rail & taxi instead !
If you need a car get a hired one! It costs more but that's the fault of the bean counters, lots of guys used to take their own car and claim for fuel but now its not allowed so we all use hired cars and still the army has to pay for fuel and hire!!! It will cost you around £50 - £150 depending on your insurance
This subject has been done to death on various threads. The requirement for business insurance is not new! The majority of policies include class A cover, which is what you need, at a very small increased premium or even free.