Smart Setup needs to be turned off first
A quick heads up for new UK Chromecast buyers that might be using it with a BT Homehub. The two might not initially play nicely together, with the Homehub prompting a "Smart Setup" wizard to display on the TV. There's no way to deal with it on the TV, but as the folks at Pocket-Lint point out, there's an easy fix.
You just need to jump into the admin menus for the Homehub and find the option to turn off Smart Setup. Once you've done that, you shouldn't have any more issues and be free to cast away to your hearts content. If you need a little direction on how to do this, hit up the source link below.