Boxtops.
If the minibus is not for ‘hire or reward’
You may be able to drive a minibus with up to 16 passenger seats using your current car driving licence as long as it’s not for ‘hire or reward’ - ie there’s no payment from or on behalf of the passengers.
https://www.gov.uk/driving-a-minibus
If there is any element of payment for driving:
Driving a minibus for profit
If you want to drive a minibus commercially, or if the above conditions don’t apply, you’ll need to apply for a minibus provisional entitlement, also known as a Passenger Carrying Vehicle (PCV) licence.