Rule 9b States:

A vessel of less than 20m in length or a sailing vessel shall not impede the passage of a vessel which can safely navigate only within a narrow channel or fairway.

So, was Fiddlers contravening this rule or any other?

NO

Why not! Because the observant among you will have noticed the 'ball' in the rigging of the Barge indicating that it is at anchor, therefore Fiddlers was not 'impeding' the Barge.

NB you will also notice that 'Fiddlers' engine is running (indicated by the triangle pointing downwards in the rigging) a safe move given the busy anchorage.