If you volunteer to drive a school minibus you are personally responsible for its roadworthiness. If any defects are found by the police, it is you who will be fined, points on your licence, or even prosecuted.
You would also be responsible for any road traffic offences committed. You should make sure that the minibus insurance policy covers:
Comprehensive insurance cover is required to ensure that you are not liable for any damage which you may cause to the minibus itself, as well as to other vehicles.
Category D1 drivers licence required
Includes tail lift
Delivery in 10 - 12 weeks