Just a thought shiznit.
Even if you decide to keep the car off the road, you need to inform the DVLA and fill out a form. And if you are driving to an MOT station, and are stopped on the way, the police must be able to confirm that your car is booked and that you are only going to the MOT station. And I am sure the insurance people also need to be advised of your situation. They sometimes get very difficult when there is an accident and the MOT is not current.
Just food for thought. My company accountant also thought there was a grace period, but he didn't check, and he let all our company cars tax run out trying to improve cashflow. We got lumbered with a fine, fairly large I suspect as no one would talk about it.
Good luck
Old Salt