I actually found one of Jem Emirali's original posts. Here it is in full including his email if you need to get in touch:
MID - The only vehicles that should be on your MID are vehicles that are taxed and your trade plates. Any vehicles in stock that are untaxed will be driven on trade plates and should not be on the MID. You are massively exposing yourself by adding them to the MID as even if the car is taken off once sold, if the purchaser does not insure the car properly and has a claim, the last known insurer may be forced to pay. Trust me when I say, you do not want a call from your broker saying your premium has gone up this year due to an accident that was nothing to do with you.
Unaccompanied Demonstration - This is another area brokers seem to be getting wrong. The only way that you can let a vehicle go out on an unaccompanied test drive is if it is taxed. You cannot lend out trade plates to customers and a customer obviously cannot take an untaxed car out on the road. The majority of our dealers with unaccompanied demonstration now are main dealers with taxed demonstrators.
Hopefully this help some of you out there but if you would like to discuss further, please email me on jememirali@astonscott.com