If you are finding what feels like a slight electric tingle shock through your fingers touching your 2019 Apple Macbook Pro or Macbook Air metal case, you need to check if the UK adapter at the end of the power supply has the metal-earth inside the slider.
I had to order two new ones and send the other adapters back to Apple, I think should do a recall, in my opinion, or send out new adapters automatically to all affected users.
Solution: The extension cable is earthed and will eliminate the problem.
The picture below shows a brand new adapter out of the Macbook Pro or Macbook Air 2019 box with no earth.
This picture shows the extension lead from a 2015 Macbook Pro with earth connection, then connected and tested with the Macbook Pro or Macbook Air USB-C power supply, and problem solved, no more shock through the fingers.