Hi Mad Steve.
I live in Cape Town and often post on the Airfix Forum and recently there was a simular post there in the general forum titled "A plea for better paint" you might find interesting. I've given up on Humbrol paints although I do still have some very old enamels of 40 plus tears vintage that still work, but the new ones or tooooo doggey to even consider. If you want a really and I mean really good matt acrylic varnish try the Vallejo one No 70.520 it brushes beautifully and sprays well if thinned but as it brushes so well it's hardly worth airbrushing. Never tried the gloss varnish but if it's the same as the matt it should also be worth a try. They might be a bit more than the Humbrol paints at about +/-R40 but at least it'll save you a return trip.
Remember we do this for fun John the Pom