Yep, spoke too soon

Started early this morning just after 6am so we could get to the Swansea bridge by 7am for our booking.  Got as far as ‘the dropoff’ which was only a couple of hundred metres and the port engine stalled.
Fortunately we weren't in the channel which made things heaps easier to navigate with one engine and we came back into deeper water and anchored for an hour or two while I tried a few things.
Symptoms are (apart from the engine stalling obviously):

• small amount of white smoke
• hard to start
• loud (much louder than normal) knocking when starting the engine [only happened once]

and it’s been quite a while (18 months) since we changed the fuel filters.
End result is I've decided that the last time I filled up I may have either got some dodgy fuel (unlikely because I’m not seeing the same issues with the starboard engine) or the tank on the port side has crud in it and has clogged the fuel filters.
Anyway, we went back to the mooring at Marks Point marina where we’ll stay for the week and commute to Newcastle via dinghy and car until we've had the fuel filters changed.  When I've got time in Newcastle I’ll set up a fuel polishing system.  More on that later.