Looking at the floor rust pics - some ain't too bad i guess, just well peeled underseal, other areas are not so nice, such as picture 5 of 7 showing the cracked rubber bush - no way can that have honestly got past an MOT tester, that is clearly beyond worn.
If you are to persuse an VOSA inspection I would also be tempted to leave the brakes alone if possible so that a true evaluation can be done on the car as it currently is.
It's just a case of how far you go with it all....even with a private sale you have cover to a degree under sale of good act etc.
It's just all the hassle and ball ache that goes with it.
If you truely love the car and think it's worth keeping, bite the bullet and re MOT it at somewhere you know and trust and see what the outcome is (gulp) then see about getting the repairs done and nailing the last MOT through VOSA, and seeing about your rights with private sales etc. Just a pain the arse innit?
Or bail out - run it into the ground and break it in the summer should get good money for interior, alloys, engine, trim, glass etc plus scrap prices are very good at the mo too

Big shame mate but your call huh?