What do you need to know? I was on the last trip (RB4) and have done the trip a few times in various boats.
There is a new round britain next year, however it is a race. Google RB12. However Scorpion RIBs ran a cruise last year, I am not sure what the size requirements were, I think it might have been 7 meters. They might run another one but havent heard.
I know RIB Mag arent planning another run, they have just done the arctic circle from scotland in a 6meter Humber Destroyer and then round scotland under 5 meter in 09. No other under 5 planned that I know, although I maybe wrong. BIBOA might have something?