Start off on a volunteer basis, get yourself a show on Hospital Radio and from there, start applying to both Independent and BBC local radio, for jobs like traffic reporting and the like. If you get lucky and get a show or part of a show, talk to your boss, tell them what you want and be prepared to accept that what you want might form just a part of the show. If it goes well, it may grow from there. Everything's governed by audience reaction. If it sells, you get to do it full time. Be prepared for it to take a while but if you believe in yourself and your talent and aptitude, you can get there. Best of luck.