A verger according to Wikipedia
'A verger (or virger, so called after the staff of the office, Latin virga = twig, rod) is a person, usually a layman, who assists in the ordering of religious services, particularly inAnglican churches'
During the service itself, a verger's main duty is ceremonially to precede the religious participants as they move about the church; he or she does not typically take any speaking part in the service itself. It could be argued that a verger's main pride during a service lies in his or her inconspicuousness; vergers often play a very prominent role "behind the scenes" — helping to plan the logistical details of service and discreetly shepherding the clergy through it. (In some churches these latter duties are handled by a Master of Ceremonies, while the verger functions as a sort of marshal in the procession.)
Now you know why he was cartwheeling, I imagine many of us would have been too!