Gulls are becoming more prevalent in urban areas, attracted by landfill sites and the increasing amounts of rubbish littering our streets. Whilst they can be a nuisance, causing damage, creating noise and mess with their droppings and even turning quite aggressive during breeding season, a licence is needed to kill the birds or destroy their nests. In fact the Herring Gull, which is the one most likely to be nesting on your rooftop has the highest conservation status as its numbers are declining.
Unless you can prove that your gull is a serious threat to agriculture, public health and safety or other wild birds, the only legal action you can take is a deterrent. There are many you can try, from bird gels to decoys, bird spikes to things that bounce in the wind.