This sounds like a classic pixellation query...
Pixellated pictures on live TV are often the sign of a signal fault. If you've rebooted your box once, then there's likely a fault somewhere, which will need resolving. When you say "all other channels that may be linked, are all ok".. which ones have you checked?
You can check for known area faults on 0800 5610061, but if there's nothing reported and a reboot doesn't solve this, then the problem is likely to either be your box or the cabling that connects your home to the streetcab.
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