If my car is SORNED and I have an expired MOT which is a month overdue can I still pre-book and drive to the appointment without being fined?
As long as you have got an MOT booked and have evidence that it is booked in such as an email confirmation which if needed can be printed. You should only drive it directly to the garage. Not fully sure that once it has passed the MOT that you will need to tax and insure it before you leave the garage or whether you can go directly home and then tax and insure it. It is a bit of a grey area I think. It might be worth checking the gov website to see the rules regarding it so if anything happens then you can be confident that you have done it right.
legally you can drive it to a pre-booked MOT and home again although that depends on what it fails on. if it is in a dangerous condition then you will have to have it repaired there or recovered (under the new rules from last year)