Extension leads are only really suitable for a temporary fix, and even then they’re not suitable for all appliances, certainly not for high-load (3kW) devices, ie those that have a resistive heating element. The whole point of Table H7 in the BS7671 On-Site Guide is to recommend enough sockets in specific rooms to ensure extension leads are not used. If they are used long-term it’s an indication that the wiring infrastructure is unsuitable, and should be adapted to suit. It will not be difficult, and shouldn’t be too expensive, to adapt the wiring to provide an additional socket that is suitable for a permanent connection for the TD and will give you peace of mind that it won’t fail, but you do need to have the work done by a reputable tradesperson.
If you’re looking to have an electrician in to do the work it may be worth asking them to fit AFDDs too.
Does that include dishwashers?
Yes.
IAAE