Voltage drop depends on the length AND size of the cable. As for will it effect what you plug into it, that depends on the rating of what is plugged in. It is not possible to be more specific as that is the only information provided.
Using 1.5 mm cable assuming 3 kW the volt drop will be around 21 volt, using 2.5 mm cable it will be around 12.5 volt, so it would need to be 2.5 mm cable, problem is getting 2.5 mm cable into a 13 amp plug is not easy, some makes will take it, but not all.
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