More digging online, and to pre-emptively answer my own question (such that anyone in the future may have a similar issue and stumble on this), very much seems like an injector seating issue.
Not sure if allowed here, cross-posting to another forumbut the below thread pretty much exactly describes it.
DEFENDER2.NET - View topic - Excess Chuff? (Possible high engine crank case pressure)
And before video (from thread - near enough to exactly same as mine):
DEFENDER2.NET - View topic - Excess Chuff? (Possible high engine crank case pressure)
And after cleaning/seating injectors:
Chuff Update - YouTube
Good thing stuck in lockdown!


 
					
					 
				
				
				
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