Multiplayer games stopped working on iPad

Mulitplayer games worked fine on our two iPad minis and iPad whilst connected to the same WiFi network until a few days ago. When we try to join a game that is running the joining machine just says "Scanning for WiFi Games" and never connects.
1) Game is started on host with "Server is visible" option set.
2) Client cannot see server game - never manages to connect
3) The same issue occurs no matter which device runs as host
4) Devices are running iOS 6.1.2