MOT Body & Corrosion Failure Cost: £150-2,000 (Often Terminal)

The MOT inspection manual draws an imaginary 30cm radius around every critical structural mounting point. Within that radius, structural corrosion (corrosion that compromises rigidity, not just paint) is an automatic fail. Outside that radius, corrosion is judged on whether it affects vehicle structure or safety.

Critical mounting points covered by the prescribed area rule:

• Suspension mounting points (top mounts, lower wishbone pivots, subframe attachments).
• Steering mounting points (rack mounting, column attachment).
• Brake mounting points (caliper carriers, master cylinder mounting, ABS module mounting).
• Seatbelt anchorage points (B-pillar, sill, transmission tunnel).
• Engine and gearbox mountings (where attached to body, not just subframe).
• Trailer towing eye attachment (if fitted).

Cosmetic rust on a wing or door bottom outside these zones is not an MOT fail. It may look unsightly but does not stop a pass certificate.

Corrosion is the failure type most likely to total an older car. The decision tree is straightforward but emotionally hard.

Step 1: Get a written quote with itemised areas. The garage should specify exactly what needs welding, where, and the labour hours. A vague "significant corrosion repair, £1,500" quote is insufficient.

Step 2: Check current scrap and trade values. WeBuyAnyCar, Carwow trade-in, ScrapCarComparison and similar tools give a current trade-in or scrap quote in 5 minutes. If the repair quote exceeds 50-60% of the post-repair trade value, scrap usually wins.

Step 3: Get a second opinion if borderline. A specialist body shop can sometimes do welded repairs more efficiently than a general garage. A second quote 20-30% lower is not unusual on body work.

Step 4: Consider future failures. A car that has welded sills today will likely have welded subframe within 18-24 months. Layered welded repairs eventually become uneconomic regardless of any individual quote. The pattern of corrosion matters as much as the current quote.

For older cars near scrap value, the MOT cost by age page covers the broader running-cost-vs-value analysis.

You cannot inspect prescribed-area corrosion from the driveway. But you can flag obvious issues that mean a difficult MOT is coming.

• Sills. Look along the sill from above and from underneath. Bubbles under paint, flaking metal, or holes you can poke a screwdriver through are warning signs.
• Wheel arch lips. Lift the wheel-well plastic liner and look at the inner arch metal. Brown stains and bubbling are the start of arch rot.
• Brake lines. Lay on the floor (carefully, with the car on level ground) and look at the brake lines running along the inside of the chassis. Heavy surface rust suggests upcoming MOT issues; pitted lines are imminent fails.
• Subframe. The metal frame the front suspension hangs from. A torch under the front of the car shows the subframe; look for severe pitting or rust holes.
• Boot floor. Lift the boot carpet and spare wheel cover. Look for surface rust progressing to actual rust-through.

A pre-MOT garage inspection (£20-50 at most independents) is usually the better option than a driveway look. It catches what you cannot see and gives you time to plan before the formal test.