@Fayre16 About 18 months ago I had a similar issue but looking at the photo you have provided it was nowhere near as bad as the issue you have.
A standard reboot didn't help so I left my Glass TV unplugged overnight. In the morning when I plugged it back in the problem had gone and luckily it never returned. Give this a try and it if doesn't help contact Sky for more troubleshooting and if necessary a replacement Glass TV (assuming it is still within the 24 month warranty).
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