The London Underground doesn't have 4G/Wifi in the tunnels. As with most things with the tube, the reason is that the infrastructure is very old and installing

The London Underground doesn't have 4G/Wifi in the tunnels. As with most things with the tube, the reason is that the infrastructure is very old and installing extra equipment inside those old, narrow and twisty tunnels is quite difficult and expensive. Here's a decent article on the topic: https://www.wired.co.uk/article/london-undeground-wi-fi https://www.wired.co.uk/article/london-undeground-wi-fi