Originally Posted by
MaxFlyer
I don’t understand why you have to go through transfer security again when you’ve already been cleared and have stayed airside.
The UK doesn't "trust" any other countries security
I suspect some of it is logisitics - you need a reconfiguration to allow some arrival streams to be processed into departures without mixing with "dirty" passengers from non trusted locations. Airports like Frankfurt and Schiphol have this baked into their design whereas LHR etc doesn't