Currently the PS4 Twitch App is not supported in the UK (or if it is they've hidden it really well).
You can watch PS4 streams via the PS4 built in streaming app.
Is there any way to watch stuff like the Loading Ready Run Magic Pre-Prerelease?
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Actually, the Twitch App is now officially available in the UK (as of 30th March 2016). You can download it from the PlayStation Store. While I haven't used it myself, the app will allow you to watch more than just PS4 relate streams.