Personally I would never cut in front. If coming up too fast and under ATC follow the aircraft in front and/or request an orbit.... the aircraft behind is responsible for spacing.
A couple of months ago I was on base about to turn onto final when cut up by some prat a*sed idiot. If he was short of fuel he should have made a pan call; if he wasn't at circuit height he should have been and if he was in a hurry he shouldn't have been!!!!