Just to add @Gray if you confident you will have no problems passing your assessment, you could take delivery of the car and have a family member put on the insurance at collection temporarily, if just for getting it home. Once you get your assessment results back you can take their name off and put yours on the insurance.
But please be as near as 100% certain the assessment will go in your favour!. There would be no problem with Mb taking the car back off you if the assessment didn’t got your way. You would get a pro rata refund of any AP you paid, but you might have to pay a cancellation fee upto £250. By the time – if this is needed you would have received the £250 new vehicle payment anyway ?