Back in the garage. Flatted out all the tiny bits in the paint that I could and gave it all a good clean and dry. Gave it another shot with the primer and the results are much better this time:
Going to let it dry overnight before giving it one final flat and a couple of coats of colour. It's not very warm outside, so it might be worth giving it that extra time to really dry properly. I'm concerned if I get too keen to finish it, there will be a mess and starting all over again doesn't appeal.