OK, so the acrylic paint isn't working for me. Not wanting to be defeated by a plastic pot of pigment, it's time to stop messing around and use proper style paint - enamel.
First step, strip off the blobby mess. A wash with Precision Paints Superstrip sorted this out. The acrylic hadn't stuck to the primer at all and came off in sheets. The stripper works well and after straining, has been returned to the bottle for use again.
After a wash down and an overnight dry, the gloss red was sprayed on. Thinned with white spirit, it worked as well as enamel does, the result being a nice shiny aircraft. OK, it took many hours to dry and needed to be covered up while doing this to dodge dust but at least it covered easily.
Life would have been even easier if the airbrush hadn't still been suffering the effects of the old paint. How the stuff can be so useless but dry to the consistency of steel inside the tiny bits of spraygun I don't know.
Anyway, now I have a gloss red 'plane. It's not perfectly smooth, but after Christmas, when the paint is properly hard, I'll try out that new buffer block I bought for this sort of job.