This is a category on your driving licence that permits you to legally drive vehicles of between 9 & 16 passenger seats. If you passed your test BEFORE 1st January 1997, you’ll automatically have category D1 on your licence.
For a detailed guide, please look at our What minibus can I drive? page
Castle Minibus can provide D1 training for all your drivers including those who have a licence issued before Jan 1997 but hasn’t been on a minibus driving course.