Sorry to post on an old thread, my questions are a little more specific to holding a USA passport in case it mattered.
As of posting Oct 2016 Is it still true that on a USA-LHR->DUB itin, one needs to get a passport stamp into the UK at heathrow, and then another stamp at dublin?
Further, How much time does this process take at heathrow? Will 75 Minutes be enough at LHR?
Thanks
75 minutes will be possible if you are on a single ticket, arriving and departing the same terminal and any bags are checked through, but it's cutting it fine. However again assuming a single ticket, the airline will put you on the next available flight free of charge if you misconnect because of immigration delays.
The challenge with a connection like this is you could easily land 30 minutes early, or equally feasible is 30 minutes circling over the Home Counties as you wait for a landing slot.