hi
I'm an airline pilot here in the good old USA and of course we are not under the CAA...however, we do NOT allow airplane movement of any kind (short of a an earthquake ;-0) while passengers are anywhere except in their seats with seatbelts properly fastened.
I am assuming that flight attendants were there and capable of reporting this to the cockpit crew? Perhaps the pilots thought the plane was ready to be taxiied...perhaps the FA's didn't do their job?
as far as reporting it...its up to you. I imagine no one was hurt, though it could have caused an injury.