Does anyone know where I can get a iPhone 6 plus unlocked from tesco mobile?
I've tried tesco, but they say they don't have authorisation from apple to do so.

Thanks

 

read this
http://www.tescomobile.com/help-and-support/1083-device-help/1102-using-your-device/unlock-your-tesco-mobile-phone

They should unlock provided you meet those conditions. If not then you may be able to jailbreak the phone and then unlock. All depends on the version of iOS you are running and if there is a jailbreak and unlock