Since you say trust, I'm assuming you're a UK student trying to shadow in a UK hospital.
The best way to shadow a doc is to literally pick one (preferably through some kind of contact - does your school know of any docs who have had students before?) and contact them. You'll still have to do all those checks though, but you would then have someone in your corner backing you up.
Most hospitals have a work experience co-ordinator as well - is it this person you've contacted? They're usually OK, though what you'll get to see varies hugely from place to place.
Better experience is to get a job as a porter/HCA/volunteer etc regularly for at least a year in some kind of healthcare setting. Looks much better on the PS, you learn more, and you get to really appreciate the less nice sides of med from early on! I'm assuming you've already lined something of this ilk up...
