Originally Posted by cikoleko
United Kingdom, if you mean was it bought from network provider then yes it's branded.
P.S. some people told me to do: fastboot oem writecid, is it correct, will it change it?
Yes, it's correct. I suggest that you use Hasoon's All In One Toolkit, though: it helps a lot automating things (avoiding command line) if you are not very familiar with these things. You can find it in the development subforum.
The point is writing the correct CID. Do you remember if your software was customized by your carrier (e.g. with carrier-related apps)? Do you have your carrier name physically printed on the phone? Not all phones sold by carriers are branded: for example, I bought it from H3G but it's unbranded.
If this wasn't the case, I would go with the generic UK CID (if exists), or with the international CID (that is HTC__001).