Just had a quick grovel and apart from the wheel arch rot (reason for failure) there is a hole at the front of the sill. Sills are generally good and better than I thought and certainly better than the Berkeley I saw earlier today.
Due to the design of the cars, think of the sills and rear arches as a long term consumable that has to be changed every say 10 to 15 years or whatever. Just like the Mk3 and Mk4 need their antifreeze changed at 11 years old for the first change.
From a corrosion engineering point of view. those say 1993 cars with no rust repairs are on the outside of the bell curve on a statistical basis.
A lot go after say 10 to 12 years, a small number before and the rest by say 15 years but in some cases you get a few lasting to 25 years.
I know of a few that have rusted through again at 5 years. One of these quick to rust again cars, when I cut apart the rear sill area, it was obvious the repairer just plated over rust.
No you cannot drive the car if it has a Dangerous Fault even there is time left on the current MOT. It would have to be trailered away from the MOT Station. Or repaired there if the MOT station also do repairs.
If the car has a Major Fault and there is time left on the current MOT certificate, you can drive it away from the MOT but if you are stopped by the police for instance, you can be charged for driving an unroad worthy car. Therefore a grey area.
If the car has a Minor Fault, it is a warning that the car is not 100% in those specific areas but is still roadworthy. Say it has 2mm of tread depth left on a tyre and the limit is 1.6mm of tread depth.
And likely the next 10-15 years for a car are considerably easier on it than the first.
10-15 years after first UK registration is a fair estimate for rust to appear. Virtually all cars you will be looking at will have had repairs done, but they could be bodged repairs, or an owner is utterly convinced he had had good repairs done, to both sills because he has the 3200 onvoice “proving” it. Personally, I’d repair what you’ve got. You can do it in stages, but I would assume both arches, sills and attendant areas will need doing.