Gulls originally lived on relatively remote sea-cliffs, avoiding man as best they could. Occasionally - presumably when their 'natural' food-supply was short - they would venture into nearby towns to take advantage of whatever they could find. Slowly but surely, they discovered that this provided easier pickings than feeding on what the sea could provide. As man's rubbish-mountain has increased in size over the years and landfill tips are scattered everywhere, the birds probably scarcely bother with the sea as a food-source any more. Consequently, you find them everywhere, including Hereford!
Am i right in thinking that they come inland whent he sea is choppy? i live in crawley in west sussex (about 30 miles inland) and the seagulls only venture up here when i think the sea will be rough. Like windy and rainy days etc.
There is no such bird as a sea gull to start with, they are gulls, they are not exclusive to the sea side, they will feed on any waste, particularly, KFC it appears judging from all the chiken bones I remove from nests in the course of my work, No im not a chicken bone remover, im a pest controler.