In reply to GridNorth: How so? He has summed things up quite well.
There is no law that says you have to have any certification to Instruct Climbing unless you are undertaking an activity covered by the Adventure Activity Licensing Act.
Competence to undertake activities can also be shown in other ways than holding a National Governing Body Award or other 'certificate':
"According to the Health and Safety Executive there are four ways to demonstrate the competence of leaders, namely: to hold the relevant national qualification, to hold an equivalent qualification, to have received appropriate in-house training or to be competent through experience"
Mountain Training National Guidelines for Climbing and Walking Leaders 1.4 pg 14
So whilst a Certificate (especially one provided by a NGB) is a robust way to demonstrate competence its not the only way. Many very experienced climbers and coaches hold no certification in climbing or coaching but have run training attended by certificated instructors (including me) and very valuable it has been. My own experience of these sessions is that they have very much been aimed at coaching performance and movement in climbers who are already competent in the skills needed in that environment (be it the wall or the crag). No attempt was made to teach ropework, knots or gear placement. In fact most of this coaching took place in a bouldering environment.
Mountain Training are also in the process of creating an award scheme for coaching in climbing. Owing to the practicalities of creating such a scheme it will initially be aimed at the lower end of the performance spectrum. How far it develops remains to be seen.