@mp10 

There was a previous user who bought a US plug and was in UK, wasn't able to change the region. What they needed to do was to create a new TP-Link ID and select the UK region.

When you created your TP-Link ID was the US region selected or the plug and your account region are both UK?

@mp10 

Prior to installing the new KP115, I already had a KP115 that I successfully installed a few months prior and was successfully set to UK, seen in the KASA app.  I can't recall if I had to manually set it to UK or it set to UK by automatically.

Also, while installing the new KP115, I do recall now that the KASA app stated that the installation had not worked, when it actually successfully installed the KP115.

In the KASA app, on both occasions, my existing TP-Link ID account was logged in and already set to UK while installing the device.  I accessed it by touching the three horizontal lines icon top left of Android KASA app screen > 'View account' > 'My Account' > 'Location of residence' > 'UK'

@mp10 

The plug should take the time zone that is indicated in the app, which the app takes from the phone. Doing a factory reset on the plug should force it to grab the right region it is in during setup.