Typically, when flying from the UK to Hawaii, you will connect through one of the West coast cities such as Los Angeles or San Francisco, and many travellers will stop off for a few days on the way in order to break their journey, and see the sights.
Flights from the main airports in the USA connect with local flights between the islands operated by Aloha Airlines and Hawaiian Airlines to get you to your final destination in Hawaii, and once there, if possible, it makes sense to take advantage of the low rental prices and hire a car in order to explore the island more fully.