Hope -
Since you're in the UK, I think the docs are under constraint as to what they can prescribe for what reasons, if they don't end up having to fob the decision off on the local alcohol treatment program. As you're still drinking, even if everything went smoothly you might end up with Namefene instead and that might not be too pleasant to adust to. Your best bet may be to go private. I'd say get ahold of Paul Turner of Alcohol Home Treatment, maybe he will have some pointers for you or maybe the name of a private doc you could see. There's one other doctor in London in the Find a Physician list, I think he charges 200 pounds for the consult and prescription.
That being said, it can't hurt to give it a go with your GP, but I'd have a "Plan B" in place. Here's a link to some print resources, note there's a tri-fold you can print too:
http://www.cthreefoundation.org/print-resources.htmlLet us know how this turns out!