Originally Posted by WHBM

The Channel islands of Jersey and Guernsey, for example, do not have any immigration control coming to the UK mainland, but do have customs, as their taxation etc system is different, which leads to many UK airports having some special passageway to allow passengers to skip the first but have to pass through the second, explaining the "Channel Islands Arrivals" notices you see. These have become a right nuisance with the further recent change in airport arrangements to prevent arriving international and departing passengers coming into contact with one another, which has led to several convoluted paths through the terminal, up and down stairs (which all require associated elevators nowadays) to go over and under one another.