There are hundreds of cycle routes throughout the UK. For a full list of routes in your area, click here.
You can't cycle on an empty stomach, but you shouldn't eat too much before you set off either. The best plan is to eat plenty of complex carbs the night before your bike ride (pasta, rice, potatoes, bread, grains) with just a little fat. Eat a good breakfast (fruit, yogourt and bread with butter or jam, for example) to give you enough energy to go the distance. While you're out, and however long you're out for, you're better off eating several small meals with plenty of lean protein (lean ham and yogourt, for example) along with simple sugars (dried fruit and cereal bars, for example), rather than eating one big meal. Avoid meat and alcohol.
Throughout the day, make sure you keep drinking plenty of water, preferably still water. You can always take fruit juice or energy drinks along too.