decided to challenge one of their senior observers on this right foot down thing. Their justification is that it means you have to hold on to the front brake and that means you're not tempted to release grip on the handlebars. This makes it safer if you get hit from behind.
This is bollocks.
Unfortunately I didn't get chance to explain the physics behind it as I was shouted down by a moron who didn't understand what he was teaching with some crap about preventing accidents and how the braking dynamics of a small and large bike are different (my comparison was the DSA technique).
If you get hit from behind whilst stationary and you're on the back brake, it'll hurt, BUT you'll probably roll forward as the back brake is limited in power and there's no real pivot point to swing around on. You have a chance of getting a foot down.
If you have the front brake on you will not roll. What will happen is that the force will be translated into a turning motion with a multiplier equivalent to the wheelbase of the bike, causing the bike to spin round and send you off. This is basic physics.
Never sit there with your bike out of gear with your right foot down. Covering the rear brake is much safer and the IAM are absolutely wrong in this - they're trying to make it faster to set off but compromising safety by doing so.
When I did my training with them, I was never forced to overtake everything in sight. If cars were doing 50 in a 60 then I stayed with them and that was just fine with them.
What I will say is that there are a lot of arrogant, self righteous people in there who are not up for discussion or debate. Anyone who is serious about making people better riders will be up for a true debate about how to ride better, even if it's just to teach people the fundamentals behind it.
EDIT: on one occasion we were sat in traffic where I felt it wasn't safe to filter. The observer (who actually had far less experience than me as well as a poor understanding of the roadcraft manual) overtook me and just left me there. It was follow her or get left behind. There are some very good ones in there, but getting stuck with a wanker just ruins your whole day.