The Lancaster - and other 'heavies' - didn't simply use the corkscrew as an evasive manouvre. It was initiated by the gunners and gave them a better shot at an attacking fighter than the fighter had at them.
I am not sure of the above statement. The reason perhaps was the gunners saw the attackers first since they were looking backwards and would warn the pilot to turn into the attack rather than guide the pilot to turn so that they (the gunners) could get a better shot at the attacker? There is no way the bomber pilot could see the fighter coming up behind the tail and therefore he relied on an alert gunner to warn you when to turn hard toward the threat.