After successfully passing my Single Pitch Award (SPA) on Friday, I took the plunge and signed up for Mountain Training Association (MTA) membership. If you have ever registered for any of the NGB outdoor awards, you should have a record with them. They recently launched a new Candidate Management System so all you need to do is register and then you can login to view your awards and your training/assessment history. You can also see your profile and allow others to see it to verify that you have the qualifications you say you have: here's a link to mine.
It cost £29 to join and I would recommend any instructors to join. Membership gets you listed on the searchable database of instructors (here) as well many other benefits and discounts. The main reason I am joining is to take advantage of their discounted Civil Liability Insurance for Instructors, which I hope to have sorted out in the next few days.