If a vehicle’s original MOT failure included any brake-related defect, a roller brake test (RBT) is required as part of the re-test then you do need a roller brake test on a retest. This applies regardless of who carried out the repair, whether you watched the work being done, or how confident you are in the result.
What the MOT Guide says
Section B.5 of the official MOT Testing Guide is clear: when a partial re-examination is carried out, the tester must examine all failed defects, check anything affected by the repair, and carry out another brake performance test where applicable, recording the results on the MOT testing service.
There is no exception for repairs carried out on-site, repairs completed by a trusted colleague, or situations where the tester personally did the work. The requirement exists because the pass certificate you issue is an independent verification that the vehicle is safe. That independence is undermined the moment you rely on assumption rather than a documented test result.
Quick summary
- Brake-related failure at the original test: RBT required at re-test, no exceptions
- Results must be recorded on the MOT testing service
- Applies whether the repair was done on-site or off-site
- Watching the repair being done does not replace the requirement