This is a common malady. On about 1/3 of my Enfield collection, either/or/and the split lock washer or collar were missing. It seems these got left out of someone's reassembly process on a regular basis.
Darren, check for both the lock washer and collar if there is play in that area. Also, the wood around the collar may have become worn eccentrically if the collar was missing or the trigger guard assembly was not tight.
Peter, you get the eagle eye award -- pretty good! (I have a bald eagle that perches in a Norfolk Island Pine across from the lagoon I live on. He can spot a small fish in the water a quarter of a mile away -- just amazing).