But the OP needs use for business cover and that is probably where the problem lies. If it is not insured for business, then it is uninsured when the OP is carrying out his work and that must be discouraged.
There are different classes of insurance for using your vehicle for work depending on what you are doing. I take a cash alternative instead of a company car and have what's called class one trade insurance. That covers me to and from another alternative place of work but no goods insurance and not for hire and reward. It does not load your premium too much. However as soon as you switch to a van it loads the premium much more.
So some from of mpv with class one may well cover it.