Sorry if I've misled but that's not quite right.
Here is an extract from the AGM 2009
From Roger Moy (FFTA): Fenlands Region suggested at last years AGM that slings should only be used to carry the rifle and not as a shooting aid. The use of a sling is contentious when employed during a designated kneeling or standing shot and removing this questionable act would certainly remove one problem from marshalling.
It was a discrete proposal but obviously it connects to kneeling.