I've been having exactly the same problem and BT have just told me that the HomeHub 2 can only handle 4 wireless connections...Apple TV was my fifth so it all started to shut down.
Basically I was losing connection on other individual connections and then all the devices connected wirelessly at the same time. Only solution was to reset the router...worked fine for 10 mins and then all the problems started again.
Has anyone experienced this? I've seen people having Apple TV wireless connection problems but this seems slightly different.
Contemplating the idea of buying an Apple Airport Express unit to act at the wireless for my network (think you can turn off the BT HomeHub wireless and connect with ethernet)...can anyone confirm that this will work as don't really want to spend anymore money but if I can get everything working I am prepared to?
I am having EXACTLY the same issue and it makes sense what you said about the 4 wireless connections because in out flat we have 5 devices and it seems to disconnect all the time with the AppleTv. Could buy an airport express and maybe turn off the wifi on the router but as you asked tommie, will this fix the issue?
Im yet another unhappy BT HH2 user that is unhappy, Mine used to do exactly the same thing.
I've now got my apple TV and iMac connected by ethernet cables and so far its been more reliable but it defeats the object of having a wifi network slightly.
I wish I had never opted for BT but hindsight is a wonderful thing .
sorry to further muddy the waters - but it's fixed for me...
I set up the port forwarding as suggested and failed repeatedly until I left out the UDP port for Bonjour.
I was then able to link the port forwarding rule to the apple TV - but it still crashed the HomeHub temporarily after 5-10 minutes.
Eventually I turned wireless encryption off from WPA+WPA2 and everything worked.
I re-enabled WPA only and have had no trouble since...
Conclusion - owing to a firmware bug the HH2 cannot handle forwarding of the required UDP port while using WPA+WPA2.