Quick answer
Rust usually fails an MOT when it weakens structural parts or affects suspension, steering, seatbelt mountings or brake line areas.
Small cosmetic rust bubbles often do not fail by themselves.
Common areas where rust can fail MOT
Sills
A common structural corrosion area.
Chassis sections
Important for vehicle strength.
Suspension mounts
Safety-critical points.
Seatbelt mounts
Must remain strong and secure.
Brake pipe areas
Corrosion nearby can matter.
Floorpan holes
May fail depending on severity and location.
Can rust failures be repaired?
- 1Welding repairs are common
- 2Replacement panels may be fitted
- 3Extent of hidden rust matters
- 4Quality repairs are essential
- 5Retest usually needed after repair
Is it worth fixing?
That depends on vehicle value, mileage, overall condition and how extensive the corrosion is.
Older low-value cars with widespread rust may not be economical to repair.