I browsed to see if I can find the answer but a search didn't reveal enough to be able to help me. This will be my first time connecting in LHR and I'm wondering how the connection will work coming from the U.S. and continuing onward to the EU (Vienna). Will I go through immigration and customs at LHR (like the US) or will it be similar to staying in non-Schengen section at AMS where it's like a domestic connection? Connection is BA to BA with an ~2.5 hour layover.

TIA