LHR immigration control for transfer
Hello everyone. This might be a stupid question, but I searched and cannot find any information.
For international transfers at LHR, I am surprised to find that passengers (satisfying certain criteria) could simply follow the purple sign and transfer to any gates at any terminals without immigration control. This is different from the USA, where every passenger must clear the immigration first.
As both the UK and the USA do not have immigration control for departure flights, I thought the procedure should be the same. As far as I know, passengers could exit airside to landside freely unless there is an "international departure zone". So, how could LHR prevent transferring passengers from entering the UK illegally?
Edit: This question has been anwsered. No need for new comments unless it changes in the future.
In short: You’ll need to speak with a member of staff airside, at which point you’ll be added to a list of people wanting to exit airside. You’ll then be escorted out by a member of staff, at which point appropriate checks will be done. There is an observation that escorts happen approximately once an hour.