Be very careful, and dont use your car to drive to the Post Office to get your tax disc.
Several years ago I was in the same situation and had to wait for the MOT to be finished before I could get my tax. I had my MOT done in the morning, and stupidly drove my car to the Post Office to get the tax disc.About a week later I received a fine of �146 (no points) for driving without tax. I was amazed because I had only driven the car to the MOT centre and then to the Post Office, and in that time someone had reported me.I suspect it was the MOT centre doing it out of spite because I had a moan at them about how long things were taking.
At the end of the day, I had broken the law and had to pay up.This was about 10 years ago so I dont know if the law is any different.