This vehicle is not a minibus
A motor vehicle with more than 16 passenger seats is not legally classified as a minibus (See; legal definition of a minibus).
If you intend to use a vehicle of this size for commercial "Hire and Reward" You will need to hold either: a Standard National Operator's licence for journeys solely within the UK, or a Standard International Operator's licence for journeys within the UK and abroad.
Charities and not for profit organisations
Charities and not for profit organisations, under certain conditions, may be permitted to operate vehicles with more than 16 passenger seats under a standard permit.