Check for International voice roaming in add-ons as well. Are you connected to a network? 

@reasonableinstrument Everything setup correctly on your account.  Pls power cycle your phone (keep it off for at least 60 seconds) to see if it help reconnect to UK networks.  Once the phone is turned back on, if it still doesn’t connect to any network pls go into your settings under ‘cellular’ and manually locate/force a network connection.  

Hi there, @reasonableinstrument!  Here is a helpful article for troubleshooting.