Be sure to use a reputable company. Hot air balloons are recognized as "aircraft" and the pilots as well as the balloon are required to be licensed. The balloon itself requires maintenance, just as airplanes do. If high levels of burner use are incurred, producing significant heat, the balloon "envelope", which is a nylon type of material, can deteriorate dangerously. The burner and fuel tanks (propane) and controllers all require maintenance. The maintenance is required to be in the aircraft logbook, BTW. Additionally, hot air baloons are made in differing sizes and can carry differing loads of people. There are sight-seeing companies here in U.A. that regularly carry ten to twelve persons at a time. The accident rate is fairly significant. As a matter of fact, an accident occurred yesterday (April 13) near Phoenix, AZ and killed a 70 year old man. Seems the winds were too high for a safe landing and the balloon struck a hilltop. As you can probably tell, I'm not very impressed with hot air balloons as passenger carriers... but at least check with your UK equivalent of the FAA for a background check on the selected balloon and pilot.... Good luck!