Update:
So the local Beek came, pumped a truckload of smoke into the hive, in anticipation of a bit of heat and got absolutely nothing. He said the brood was looking terrific and there was no disease
. He even marked the queen for me. His view is it’s the Messmate Stringybark setting them off. While they flowered last year, it wasn’t nearly as heavy as it’s been this year - there really is a strong honey smell to them this year, whereas last year was a bit meh. He also correctly suspected that my nervousness around the hive (because of the increasing agro) wouldn’t have helped, as well as the dull/overcast weather during the last two inspections.
Without being 100% sure, he said something like, stay away from the hive in the morning and early part of the afternoon (I think). Can anyone clarify? We went in at about 4pm on a sunny afternoon.
I got chased away from the hive the next morning when feeding the chooks, so I guess it all adds up. My addition was obviously a bit out before that. I’ve found a couple of online references to bee aggression with messmates:
Amongst beekeepers it has been known as the 12 day wonder, producing large quantities of nectar during its peak flowering period. The nectar tends to make the bees defensive and protective of their colonies (aggressive). The pollen is good quality and bees breed well on it.
From Heathmont Honey - Messmate - Eucalyptus Obliqua
Flowering started early this year, however, many still haven’t started, so this could go on for a while 
Anyway, a good result and I didn’t have to squish the queen! Thanks again to everyone for your help and feedback!