I don't think it spoke the first one or two times I pressed the button. Does the speaker icon stay pressed for a few seconds as if it is playing? Make sure your volume is all the way up and put the speaker to your ear. Any hissing noises as if it's trying to play something?
If it's still not working, try re-installing the app. Otherwise, it may be your location as you suggested.
Yes i was connected via WiFi, but it's just started working now. Thanks for your replies guys, don't think i'm missing too much by the sound of it anyway, was just curious why it wasn't working. (It is now)