One option is to use powerline adapters (not WiFi extenders) to extend the ethernet connection over the mains e.g:-
Alternatively, buy a longer cable.
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If the ethernet cable provided is not long enough to reach the TV box, there are a number of options. You can use powerline adapters to send the signal over the electrical circuit of your home, or alternatively a better option is to use a longer ethernet cable.
We do not provide these but you can pick these up in electrical stores or on line from places such as amazon.
Depending on the length you need, as a guide, these are approximately £1 per metre.