not always just getting a new passport, cant speak for the uk but in the us they have electronic notes. i guess you didnt realize they scan that passport of yours everytime you exit and enter the country.

having certain countries in your passport that for a lack of better words, arent in the best of relations with the united states, can and probably will cause "delays."

this also applies to countries that arent your home, travel to israel with any terrorist supporting countries in your passport you might just find yourself in a room being asked a few extra questions...