3G signal active on "raw" restore - gone after backup

Hi everyone,

I have had a good look on here and Google for a solution to this problem but no luck!

I have recently bought an iPhone 4, it isn't jailbroken and hasn't had a carrier unlock. I restored it as a new phone over iTunes and noticed that I had full signal, 3G was on and everything looked normal. However, after restoring from a previous iPhone 4 backup (also not jailbroken) from last week I have lost 3G signal.
My carrier (3 UK) can't help either.

The previous iPhone backup was from a phone using iOS 6.0, the restore was done using 6.0.1

Thanks for your help :)