iPhone 8 Time Zone Errors

I have an iPhone 8. I have disabled the Set Automatically slider in Time and Date and set the Time Zone to London. I travel extensively so move between several time zones. Every time I turn the phone on the Set Automatically slider resets itself to ON thus moving my phone to a new and unwanted time zone. I queried this at an Apple Store but none of the technicians could help. It is imperative that my Time Zone remains on London and the anomaly whereby Apple thinks it knows better than me what time zone the phone should be in is disappointing. This error has been present for each of the iOS iterations since the iPhone 8 was released and it remains thus with the latest 11.1.1. Does anyone have a fix for this bug. Apple?