AirPlay icon not appearing on ipod touch

I have an iPod touch 4th generation with iOS 5.1.1 and an Apple TV 3rd gen with OS 5.0.2. They're both connected to the same router and signed in to the same apple account but I can't get the AirPlay icon to appear in any of the apps on my iPod touch. AirPlay is enabled on the Apple TV.

I've read the troubleshooting guide but it's no help. There are no suggestions other than check both devices are connected to the internet. There is no suggestion of opening ports on my router that I could see but this is the only thing I can think of trying. But which ports?

The Apple remote app doesn't work on the iPod touch to control the Apple TV either.

Any ideas?