There are multiple ways to handle this that work in the UK as well as the US.
Many people use the third-party service, life 360. I believe that also works in the UK. But not everyone likes that, because it would allow you to track the other person and they might not want that. So you succeed in locking them out of smartthings control, but they might feel they had given you too much information.
The SmartThings arrival sensor fob is an obvious alternative. No privacy issues and no tracking.
If you have a housemate or a teenager or a dog walker or someone that you want to have access to some SmartThings control but not account manager level access, the third-party smarttiles dashboard app is very popular. You can customize it so that the person only has on/off control of a specific set of devices but they can’t change any of the routines or access other devices. It was originally developed by a community member who didn’t want one of his children to be able to turn off the lights and the other child’s room. 
It Has since grown to become a very polished offering. It has no presence tracking, however, so you have to combine it with one of the other presence methods. But it does solve the problem of giving someone limited access to SmartThings device control.
There are some other presence options as well. The following FAQ should be of interest: