The photos don't offer any way to prove that, but they do show a retail box which looks authentic:
While I am convinced that a larger iPhone will be launching next month, and I would even be willing to accept that beta units are floating around, I simply don't find it plausible that one would come with a retail box. There's just too high of a chance that the box might be left sitting around to be accidentally discovered, photographed, and shared online. So I seriously doubt Apple would be shipping it to testers.
Furthermore, theTechRadar photos don't show any screenshots, so there's no way to know for sure that this is a real iPhone 6 and not a Chinese-made knockoff running Android. I haven't been reporting on the knockoffs, but I have been following the news and some of the iPhone 6 clones are quite nice.
At least one model even comes in a retail box which says iPhone 6 and sports a surprisingly realistic home screen. Alas, the Google Play app gave it away:
Don't get me wrong, I wish the photos shared by TechRadar showed a real iPhone 6. But they probably do not.