O2 vanished!

I have searched every where without finding anyone with a similar problem.

I have lost the "O2-UK" in the top left hand corner of my screen! It still shows the signal bars and the 3G symbol (when present) but not the network name. I can use the internet, receive & make calls and access my voicemail all as normal. I was recently in the Lake district and lost my signal....when it returned the network name didn't!

Any ideas greatly received!