Must be a Brit thing.
I have only been involved in Aikido since 1994 here in the States. This is the first time I have heard of actual combat style competition (like Karate and Judo).
So far as I have experienced (take that as you will), we have to take turns being the aggressor. I have never seen two aggressors matched against each other to make a combat competition.
Clarification would be appreciated.