Cjando, I was intrigued by your solution so called Sky this morning and they talked me through it. Incredibly this simple step solved the problem. Many thanks.

So this is it: when you get to the final blue screen, where it says you are watching Ultra HD 2160p 8-Bit, you simply have to confirm the settings and then press the home button to go to your 2160p picture. In other words, you will not be able to see the 2160p picture when you have to confirm the changes, you only see a blue screen. You just have to trust that all is ok. Shame that sky didn't tell me this before.