How can I become a support/guide dog trainer?

I'm currently considering a change of career, and trying to find information on how I might go about it. At the minute i work in a completely unrelated job, but my passion has always been animals and I regret not following this path earlier. I spend my spare time volunteering with shelter dogs, and looking after/walking people's dogs for them. I'd like to get into dog training in the support field, and gave been looking at Guide Dogs and of course Support Dogs here in Sheffield.

Does anyone know how I would get some experience in this to see if it is for me (even just with dog training in general)? I've looked at volunteering opportunities, but they tend to be around fundraising or fostering (which I can't do). Is there any way to get the chance to see how these dogs are trained, before I jump into getting qualifications?