Thanks Alistair. I will have to re-read what you have written in the morning when I might have a chance of understanding it.

The key thing is that I want rid of Sky because it costs. For that matter it goes against the grain to replace the existing TV when its still working.
I dont like paying. So I am happy for the most part watching BBC, ITV, C5 C5 and freeview. But none of the media streaming devices seem to mention these channels. What, for example, does the Amazon Fire allow you to watch? Presumably it feeds from my router via a cable and then to the TV. Correct?

Then what do I do about the TVs in the other rooms - kitchen, bedrooms etc? They have a feed from the terrestrial aerial so it would be handy if I were able to feed TV from the internet router into the cables built into the walls already, the router signal being wek in the bedrooms.