How Should Our Landlord Notify Us Of Changes To Our Agreement?

10 of us share a flat and rent individual rooms from our landlord with shared communal spaces that we are all responsible for. If the landlord wants to change something (for example he just implemented a policy of charging a retainer on the summer holidays if the property is empty) should he inform us all individually or can he rely on telling one person and assuming the rest will be told? We also pay our rent by the term (11 weeks), how far in advance does he have to notify us of changes? Thanks