As Bednobs indicates, you have never held a passport. Your school held one, with your name on it, but that doesn't count as 'your' passport. (I've got several old group passports, as mementoes of my teaching days. They were valid just for specific trips).
Remember to allow plenty of time for your passport application because all applicants for a first passport now have to attend a passport centre for interview. Full information can be found here:
http://www.ips.gov.uk/passport/apply-first.asp
Chris