Have a look on TV companys' websites or ring them up, like channel 4, Sky, ITV and MTV. Or look for contact details on TV shows. The important thing is usually having a specific name to write to or contact, so if you call ask who would be the best person to speak to regarding work experience. Most usually run work experience programmes, or have details of who to contact about possible opportunities. For radio try Radio 1 website, or you could try emailing a DJ. It sounds unlikely, but i've heard them mention on the air when it people have done it and it worked. For film, contact production companies to see if any films are being shot in your area. My mate got experience on a channel 4 film in manchester this way. It'll be likely to be really low budget, but you can get really good experience being a runner or something. A method that has worked for me is contact as many places as you possibly can, pick places that you think will have a creative environment, and be open to new ideas and giving people a chance, just make sure you are really enthusiastic, except you won't be given the best stuff to do, but critically don't look like you might cause them any trouble. Good luck!