A cracked plate is not an automatic failure on its own. It fails if the crack does one of three things: makes the registration illegible, leaves the plate so insecure it is likely to fall off, or amounts to excessive damage, deterioration or delamination.
If it does any of those, it is a Major defect, and every Major defect is an automatic MOT fail.
What the MOT manual actually says
The MOT inspection manual lists exactly four things that can go wrong with a registration plate. There is no Minor category for any of them, so all four fail the test outright.
| Defect | Category |
|---|---|
| Missing, or so insecure it's likely to fall off | Major |
| Inscription missing or illegible | Major |
| Showing an incorrect registration | Major |
| Doesn't conform to the specified requirements | Major |
A cracked plate usually gets caught by the second or the fourth. The manual is explicit that plates must not be "excessively damaged, deteriorated or delaminated".
When a crack will fail
- It runs through a character, or close enough to make one ambiguous
- The plate has split into pieces, or a corner is working loose
- Water has got in and the reflective layer is lifting or bubbling around the crack
- The plate rattles or flexes when pressed
When it might pass
A small crack at the edge, away from the characters, on a plate that is still firmly fixed and perfectly readable, may well pass. The manual tells inspectors to reject characters only "if obviously incorrect", so a tester is not hunting for hairlines.
But that is a judgement call made by one person on the day, and a different tester can reasonably reach a different answer. If you are relying on it, you are gambling a retest fee on someone else's opinion.
The one people miss: delamination
Delamination is the reflective layer separating from the backing. It shows up as bubbling, cloudiness, or a milky patch that spreads from an edge or a crack, and it is extremely common on plates more than a few years old.
Owners rarely notice because it happens slowly. Testers spot it immediately, and it fails under the same "excessively damaged, deteriorated or delaminated" wording. If your plate looks hazy or patchy rather than cleanly reflective, that is what you are looking at.
It isn't only about the MOT
A plate that does not display your registration correctly can bring a fine of up to £1,000, and the registration itself can be withdrawn. That applies the whole time the plate is on the car, not just on test day. You do not need to be due an MOT to be pulled over for it.
Which is the practical argument for replacing a cracked plate now rather than at the next test: a replacement costs less than the retest, and a lot less than the fine.
REPLACE A CRACKED PLATE
Road legal, made to BS AU 145e, posted free across the UK. Enter your registration and see it before you buy.
Order a replacement