We will arrive from Australia at Heathrow and the same morning fly out to Dublin on a different airline. In Dublin we hire a car and drive around Ireland, ending in Belfast. We have booked a return flight from Belfast City Airport back to Heathrow to continue our holiday in England.
I presume we will have to go through immigration and baggage collection when we arrive in Heathrow the first time and then check in with the other airline to Dublin. What happens when we get to Belfast Airport as we will not have gone through any border security between Ireland and Northern Ireland in our hire car. Are there immigration facilities at Belfast City Airport or do we go through immigration again when we get back to Heathrow, even though we will be on a domestic flight? Or do we ask for some re- entry documentation the first time we are at Heathrow?