Dave
I think you had better check with your insurance company that the "for business use" actually covers the cost of equipment that you carry. I think you will find that it doesn't and it only covers your vehicle and 3rd party property when you go from place to place while you at work. If my memory serves me correctly, this 3rd party property is other cars, walls etc and not specific equipment carried. After all if you add up the cost of your test equipment and maybe some medical devices, it probably adds up to more than the value of the average small car. they tried to get us to sign up for this responsiblity in both the NHS jobs I have done and after checking with several insurance companies, none would cover equipment carried belonging to someone else.
Graham