As a general rule, a warning light in the instrument display will be a fail point if it indicates the failure of a component that is also part of the test procedure. For example, an ABS warning light or headlight main beam warning that is illuminated likely means that those systems are not functioning correctly, which would also mean a fail.

Unfortunately the MoT inspection manual doesn't provide a comprehensive list of warning lights that would cause a failure, and as the SBS system is a safety item it may well result in a failure.