simon mitchelmore wrote

Does anyone know if the USB charger is permanently
energised (when fitted as part of 13A sockets)

Yes they are.

or whether it's turned on via a micro
switch when the USB plug is inserted

They hardly ever are.

(I'm guessing the former)?

You are correct.

I know the current draw of a USB charger is tiny when
open circuit but, being 'old school', I always remove
the USB lead plug when not charging our phones

Mad waste of time. I only do that in the car
because the lead gets in the way and I only
charge in the car very rarely, only on long trips.

but this may be the cause of several USB leads becoming faulty.

It can be depending on whether you unplug
it by holding the USB A plug or the cord.

The cheap cords dont last all that long.

Maybe I should leave the USB leads
connected permanently and relax?

Yes you should.