Default RUU File

Right I am currently rooted on a htc one, but am looking to return my phone back to everything being stock to sell.

I have read numerous how-to's on how this is done, but there is one thing that is confusing me and that is choosing the correct RUU file for my set-up.

I have tried 2 or 3 now and have had no luck what-so-ever so was wondering if anyone out there can shed some light on the matter.

I am on the network '3 mobile' and reside in the UK.

I have located a list of RUU files (http://forum.xda-developers.com/show...php?p=39588860) but am struggling to determine which one is correct.

Would really appreciate someone pointing me in the right direction or pointing me to the correct RUU file as it were!