Why can't I update my Nexus 4 to Lollipop?

As I understand it, Android Lollipop (5.0) is now generally available over-the-air. My Nexus 4 briefly offered for an hour or two to install it. I said yes, and watched it start to download. When I next went to unlock my phone, it obviously wasn't installed. Now, when I go into the Settings app, and manually check for updates, it says my phone is up-to-date. It's still on Android 4.4.4.

I don't particularly want to install the developer image, as that'll wipe all the data from my phone. Is there any way I can encourage it to update?

I'm in the UK, if it's relevant.