I'm looking into: flying into LHR (arrive T3), then switching airlines and terminals for another flight (T5) a few hours later. Because this is not one booking/airline/terminal, how much time should I give myself to: arrive, go through immigration, claim my luggage, go from T3 to T5, check in, and go through security (again). Also, what is the fastest way for someone with a lot of luggage to go from T3 arrivals to T5 departures. Hope this wasn't too confusing! :) Thanks in advance!
http://www.heathrowairport.com On the left will be a menu.One says "travel between terminals." Click on that and scroll down to the one you want.
would that work though for going from T3 Arrivals to T3 departures?
Spare yourself AT LEAST 4 hours. As you probably know, in case of severe delays on your incoming flight, you are essentially on the hook for anything concerning the 2nd flight.