I'm changing planes at LHR soon. My incoming flight arrives at T3, and my departing flight is from T5. If I bring duty-free alcohol in my hand luggage from my initial airport of departure, will it be confiscated when transferring terminals at London Heathrow?
When you buy duty free it is in a sealed bag. As long as it remains in this sealed bag it should be fine unless there are some specific extra checks at Heathrow that I'm unaware of.
From my personal experience: No it is not possible because of security checks at T5.
This experience is a few years old, but security rules became more strict the last years on not more relaxed - so I won't assume they abandoned this security check.