Why is this incidentally? The planets from my understanding cycle through all the zodiacal constellations so Mercury "ought not" to be more easily visible from the southern hemisphere.
I have seen it a few times, perhaps 4 or 5 - invariably on spring evenings.
It's to do with elongation from the sun.
Mercury can reach 28 degrees from the sun, but only 18 degrees sometimes, because of the ellipticity of its orbit (Venus has a nearly circular orbit and regularly reaches 47 degrees).
It turns out that northern temperate latitudes get the 18 degrees and southern/equatorial latitudes get the 28 degrees.
On the other hand, Mercury is brighter (a full magintude) when closest to the sun, so we get brighter but closer to the sun in the sky, so one effect compensates the other.
You have a week-10 days either in spring (evening) or autumn (morning), and you need a really clear sky down to the horizon.
...and I was above the clouds with an unhindered view from on board Jacqueline Gold's Beech 200...
The full story can be found in the link below:
( Apologies, moderators - the article is a .pdf and doesn't let me quote from it )
Peter, I'm a BAA member too and have just re-read your "trip report" from the Journal.
Looks like we were both very lucky that day, I was near Reims in France and was very fortunate to get a clear view from first to fourth contact.
I also had a good view from deepest Idaho in 2017.
It's amazing what specialised equipment people bring along - compared to my humble 300m lens and camera on a tripod.
Even the traffic jam afterwards was enjoyable...