If you don't fancy reading all the MOT manual then > Appendix A Structural integrity and corrosion >3 Corrosion assessment
link clickyhowever, it is more complex than just quoting one section of the manual
plus, it sounds like the failed car did have quite a bit of rust in prescribed areas etc, and having family members drive around in cars that are swiss cheese and may become dangerous in the 12 month period before next MOT is not a good idea
(particularly as your checking the car BEFORE presenting it for MOT Terry, so, effectively if the NT misses something, and you say it's ok or miss something, then it fails , that family member will remove you from the Christmas card list
)
as an example, the Zafira I just checked over, it came with MOT till mid March 2019, the last 2 MOTs are pass,no advisory notices on the printed certificates.
Knowing that family members would be transported at speeds up to 70NPH ,I checked it all over ,decided the brakes looked poor, not maintained, so I stripped, cleaned, fitted new discs and pads, found a brake line badly corroded and it leaked ,so replaced that in it's entirety.
I'd checked the MOT history and it failed 2017 on Nearside Rear Brake pipe excessively corroded (3.6.B.2c)
Offside Rear Brake pipe excessively corroded (3.6.B.2c) ,the same day the MOT pass with no advisory notice was issued, so I'd assume the brake pipes had been replaced, yet they where all original.
I spend a lot of time checking the family fleet, to
try and ensure all is safe and reliable, it would be much cheaper and less hassle for me to just say "take it to a garage" have them do anything that is needed.
Sadly, SOME garages charge for things they don't actually do, miss things, do jobs badly, some jobs are not part of MOT testing.
so I've developed a lack of trust