You can only take train driver Psychometrics 3 times in your lifetime. Used to be 2 attempts.Regardless of what you achieve in any test and with any TOC/test provider.
It has to be that way, if people had more attempts they would pass on familiarity rather than ability. Most people who pass and get the job they apply for would have no further reason to retake the test, like for a mainline job etc.
Others may only reach national standard but the TOC they applied for requires enhanced. Or to be a depot driver (Non European License Holder)
Whether you achieve National, Enhanced or Fail, you use an attempt/life.
I passed them to become a depot driver, applied to become mainline within the 5 year validity of my test and they accepted my enhanced pass mark and only made me take a fault finding test. Had I applied and had to do the tests again whether they wanted me to or because id gone past my 5 years, had I failed that would have been it for me. At the time i took them it was 2 attempts.