We are arriving on BA in Terminal 5 Heathrow for a 5 hour layover (from LAX) before departing from Terminal 5 to Cape Town on BA. We would like to relax in one of the lounges in Terminal 3 because we have a Priority Pass or an American Airlines Admirals Club Card. We are flying Premium Economy, so do not receive access to the BA lounge in Terminal 5. Can anyone offer advice? How difficult is it to get through immigration and make our way to Terminal 3 and back in 5 hours? Any information regarding this would be extremely helpful! We are flying May 11, 2014 .