UK health sites and forums

I've found a website called healthtap. It's a great Q&A forum. Most of the doctors are American though and I want help with something which is not particularly a health problem but more procedural and to do with going the actual GP.
So... I have a particular health issue which has a large number of causes. These causes can be diagnosed by a variety of tests ranging from endocrinal (thyroid being one of them) to a various different blood tests.

1) I want each of these tests to be carried out to pinpoint which is the culprit cause and I want to the dictate this to the GP otherwise I know I will get a generic answer and a generic prescription or course of action.
Can I do this?

2) When a sample of blood is taken I know there are many types of blood tests e.g Blood Glucose Test, Full Blood Count... I want a few
specifically. Can they these few tests all be done with the same blood sample the nurse takes with the syringe or does she have to withraw blood 4 times?

3) Are there any UK forums like this one which focus specifically on health and have some medically trained professionals as members?

With the first bit I'm saying if I go there and tell him the problem he'll give me some generic prescription and send me on my way- that's always been my experience with the GP. What I want to do is go there, tell him: Buddy I've googled this extensively- it seems these are all the possibilities for what's causing this problem. I want blood tests taken, urine samples, stool samples, breath tests, whatever to test for these causes and see which one or which few even it is. Can I be assertive in that way with the GP? I don't want to walk away unsatisfied knowing his suggestion isn't gonna be the best way.

No, your GP decides what tests they want you to have. They may or may not be the same as what you want. Googling extensively does not replace a medical degree.

I don't think it is though. If it is a specialist they will know that specific area inside out and you have no chance of competing with that knowledge but everything you need is online. Sadly the tests have to be done at the GP though.