A method of authorising a user of a communication system to be added to a group communication event comprising: creating, by a host node associated with a host user, a conversation group by selecting a group of users of the communication system; transmitting, by the host node, a group creation notification message to the group of users of the conversation group, the group creation notification message comprising a conversation group identity and a list comprising the identity of each member of the group of users; initiating from the host node, the group communication event with the group of users by transmitting a notification of the group communication event comprising the conversation group identity; responsive to receiving, by the host node, a group communication acceptance from at least a first user in the conversation group, establishing, by the host node, the group communication event with the at least first user in the conversation group; displaying, in a user interface of a client executed at a user terminal of the at least first user of said group of users, an identity of each member of the group communication event in response to receiving the group creation notification message; receiving, at the host node from another user of the communication system during the group communication event, a communication set up request for setting up a communication event, the communication set up request comprising the conversation group identity; analysing, by the host node, the communication set up request to determine if said communication set up request is associated with said group communication event initiated by the host node, said step of analysing the communication set up request comprising determining if said other user is a member of said group of users, and determining that the conversation group identity is present in the communication set up request; and if it is determined, by the host node, that the said other user is a member of said group of users and that the conversation group identity is present in the communication set up request, adding, by the host node, said other user to the group communication event. creating, by a host node associated with a host user, a conversation group by selecting a group of users of the communication system; transmitting, by the host node, a group creation notification message to the group of users of the conversation group, the group creation notification message comprising a conversation group identity and a list comprising the identity of each member of the group of users; initiating from the host node, the group communication event with the group of users by transmitting a notification of the group communication event comprising the conversation group identity; responsive to receiving, by the host node, a group communication acceptance from at least a first user in the conversation group, establishing, by the host node, the group communication event with the at least first user in the conversation group; displaying, in a user interface of a client executed at a user terminal of the at least first user of said group of users, an identity of each member of the group communication event in response to receiving the group creation notification message; receiving, at the host node from another user of the communication system during the group communication event, a communication set up request for setting up a communication event, the communication set up request comprising the conversation group identity; analysing, by the host node, the communication set up request to determine if said communication set up request is associated with said group communication event initiated by the host node, said step of analysing the communication set up request comprising determining if said other user is a member of said group of users, and determining that the conversation group identity is present in the communication set up request; and if it is determined, by the host node, that the said other user is a member of said group of users and that the conversation group identity is present in the communication set up request, adding, by the host node, said other user to the group communication event.