We draw on many great teachers and sources of knowledge. Every recommendation below is someone I have trained with, or a book I have read. I have no financial incentive to make these recommendations although if you buy the books or kit via the Amazon link I will get paid a (small) amount.
Iain has been on the grading panel for every Dan grade awarded at our club and its forerunner. We go to his seminars, follow him on YouTube and subscribe to his app. We also all his books and DVDs. Iain is the place to start for practical karate.
Peter is the founder and principal of the World Combat Association, British Combat Association and the British Combat Karate Association (with whom we are affiliated). Peter is one of the world's foremost authorities on practical martial arts, and a great guy to train with. If you ever get the chance to train with Peter, you should jump at it.