After tethering with iPhone, apple tv won't connect to other wifi networks

My Apple TV, v3, has previously been connected to my home broadband wifi router (and more recently my airport extreme), however when I moved home I tethered it to my iPhone 5 (and more recently 5s) to connect to the Internet. I can only assume that since the last software update on the Apple TV (and iOS 7 on the iPhone) something in the settings has changed, as my Apple TV will no longer connect to any other wifi router. I've tried the supplied Virgin Wifi router and I have an Airplay Extreme. In both instances, the Apple TV connects to the wifi, however tells me there is no internet connection available and that I must configure the Ethernet settings.

At the same time, I also have a Humax 1010s Freesat box, and exactly the same thing has happened. It will tether with the iPhone, but will not connect to any other wifi sources, telling me there 'is a problem'.

I am open to ideas/recommendations, to resolve the issue - you can't imagine how frustrated I am with Apple right now... And it seems too coincidental that they both stop working around the same time yet both still tether to my iPhone whilst refusing other wifi connections.

I also have another Apple TV, V2, that I have not tethered and it works fine with my airport extreme, as does my iPhone and iPad.

Thanks in advance for any help anyone can offer!