He was actually banned because of his views on violance ie attack frst not because he teaches lethal techniques, we have plenty of instructors who can and do openly teach that here. He was planning to tour the areas where the riots were to teach people to attack before they were attacked themselves therefore it was considered inciting violence.
The other thing of course is that he was coming here to work. As I said we have plenty of instructors here who can teach techniques so the Home Office may have considered he was taking a British persons job, I know many countries have this rule as well. Even well known personalties coming from other countries to perfrom here have to jump through the hoops to get a work visas. I know it's the same in the US because my son in law worked there for a while, he got in because British trained racing stable staff are considered to be more specialised than local ones. He and my daughter were going to work in Florida for a season but that year because of the weather ie Hurricane Katrina, the New York racing people didn't move down to Florida so there weren't any jobs. They were told by the American Embassy that the rules were that they had to have jobs that the locals couldn't do.