You have to apply. Also will need a passport type photo. Sometimes your local council will take a photo (if you turn up in person, obviously!) or you'll have to send a couple in with your application form. Give them a call - number in the phone book - and ask 'em exactly what is required. Let's hope your local public transport is better than where I live! Good Luck!
One of my sisters went to apply for her bus pass, armed with a photo. She was sent away as she didn't have enough I.D. with her, such as driving licence, passport and utility bills. This may not be the same for all counties, but as long as you are aware you may need them.